Paratarbus carbonarius Petrunkevitch Scientific Papers, State of Illinois, 1945, Vol. III, No. 2, pp. 25-27, Plate II, fig. 11, Text-figures 5 and 6. A single specimen from the Pennsylvanian of Mazon Creek, Illinois, in the Illinois State Museum. Key to the European Species of Architarbi 1. Carapace evenly rounded in front, with a straight posterior edge. Phalangiotarbus subovalis Woodward. Carapace pointed in front 2. Carapace longer than wide ... - Carapace wider than long or as wide as long .... 3. Carapace with a trifoliate eye-tubercle bearing three pairs of eyes. Abbreviated tergites each with a pair of tubercles situated close together. Mesotarbus intermedius n. sp. Carapace without tubercle or eyes .... 4. Width of body one third of total length. Anterior two tergites sinuous. Leptotarbus torpedo (Pocock) sub Geraphrynus. Width much more than one third of total length. Anterior 5. Carapace with a trifoliate eye-tubercle bearing three pairs of eyes. Abbreviated tergites each with a pair of tubercles situated close together. Posterior edge of carapace angulate. Goniotarbus tuberculatus n. sp. Carapace either without eyes or (secundum Pocock) with 6. Posterior edge of carapace sinuous Posterior edge either angulate, or procurved or straight 7. Last two intersegmental tergal lines form an angle directed with the apex forward. Pocock's species angulatus (sub Geraphrynus). Last two lines gently recurved. Pocock's species hindi (sub 8. Posterior edge of carapace straight. Two last tergal intersegmental lines form an angle directed with its apex for 2 35 4 6 78 ward. Waterlot's species kliveri (sub Opiliotarbus). - Posterior edge procurved. None of the tergal lines angulate in middle 9. Posterior edge of carapace angulate. Abbreviated tergites each with a pair of tubercles situated close together. A single pair of eyes, according to Pocock. Pocock's species tuberculatus (sub Geraphrynus). Posterior edge of carapace not angulate, but evenly curved. 9 NB. The Genus Eotarbus Kusta is not included in the above key for the following reasons. Kusta (73) listed on p. 7 of his article in 1885 under No. 14 a specimen under the Genus Architarbus with a question-mark. In 1888 he named it Eotarbus litoralis and gave a figure of it. He gave no description of the specimen which, according to Fritsch (23) has apparently been lost. Haase regarded it as an architarbid, but Fritsch believed it to be an insect larva. The figure resembles an Opiliotarbus, but without a description of the specimen and in view of its loss nothing can be done about it. 2. Family OPILIOTARBIDAE, 1945 The characters of this family are given in the key. A single genus belongs to it. Genus Opiliotarbus Pocock, 1900 Type O. elongatus (Scudder), sub Architarbus Pedipalpal coxae not visible. First pedal coxae in contact with each other in the median line along their full length. Carapace evenly rounded in front, with a straight posterior edge, wider than long. Eyes wanting. A single species. Opiliotarbus elongatus (Scudder), sub Architarbus, Mem. Boston Soc. Nat. Hist., 1890, Vol. IV, p. 449, Plate 40, fig. 4. Pocock, Geol. Mag., 1910, Vol. VII, p. 511. Petrunkevitch, 1913, Trans. Conn. Acad., Vol. 18, p. 131, Plate XI, figs. 62-65. Text-figures 85-88. Two specimens from the Pennsylvanian of Illinois: the type, No. 37975, from Mazon Creek; specimen No. 37970 from Braidwood; both in the U. S. National Museum. The specimen from Belgium, referred to this genus by Waterlot in 1934 under the name of O. kliveri does not belong to it. Its trochanters are not known, its carapace is triangular, the number of its tergites is given as nine. These are characters found only in the Family Architarbidae, q.v. 3. Family HETEROTARBIDAE Petrunkevitch, 1913 This is an aberrant family with some characters resembling Opiliones and others Architarbi. It is represented by a single specimen. Genus Heterotarbus Petrunkevitch, 1913 Type H. ovatus Petrunkevitch Heterotarbus ovatus Petrunkevitch, Trans. Conn. Acad., 1913, Vol. 18, p. 115, Plate X, fig. 59, Text-figure 70. The specimen is from the Pennsylvanian (Lower Allegheny) of Mazon Creek, Illinois, and is in Mr. L. E. Daniels' collection. No other specimen has as yet been found. 5. Order ACARI The great majority of Recent Acari are minute animals. A single Paleozoic species, Protacarus crani, has been described so far by Hirst from the Devonian Rhynie Chert Bed of Aberdeenshire. Hirst gave several excellent figures leaving no doubt of the affiliation of these fossils. The size of his specimens varied from 290 to 440 micromillimeters. It seems strange that the much larger representatives of the Family Ixodidae having always a very tough skin which resists mechanical injury, have not yet been found in the Paleozoic. Recent Ixodidae are visiting parasites of Vertebrates, mainly of Mammals and Reptiles. Recent Acari are either parasitic, terrestrial or inhabitants of fresh- and sea-water. Modern Acarologists are inclined to split the Order Acari into sev eral Orders. Oudemans has even attempted to split the single Order Acari into several groups to which he gave the rank of Classes. His classification is based on the movability or immobility of the coxae, a character which exhibits remarkable fluctuations in other orders of Arachnida. When, as in scorpions, in the same individual the first two pairs of coxae are movable and the third and fourth pairs are permanently fused on each side of the body, the use of the state of mobility as an important character is quite unwarranted. The raising of Suborders to the rank of Orders is quite another matter, for they are well defined in their characters. Yet I think that they show sufficient characters in common with each other to necessitate their retention in a single Order Acari. The Order shows a tremendous amount of variation in structure and habits, presumably correlated with parasitism. The interested reader is referred to Count Herman Vitzthum's ACARI in Kükenthal's Handbuch der Zoologie, 1931. Volume 3, second half, pages 1-160 with an extensive bibliography. II SUBCLASS STETHOSTOMATA, new In this Subclass are united the only two Orders of Arachnida in which the arrangement of the coxae is similar to that in Xiphosura and Eurypterida and, therefore, unlike that in all other orders of Arachnida. Morphologically anterior to the pedipalpal coxae, the chelicerae are in reality situated above them in all Arachnida except the Stethostomata. In the latter all six pairs are in the same plane and, in addition, the coxae of the three-jointed chelicerae are so wedged in between the coxae of the pedipalpi that the mouth, to be functional, had to move backwards until it became situated between the coxae of the first pair of legs, behind the posterior ends of the cheliceral and pedipalpal coxae. The abdomen is broadly joined to the cephalothorax and its first segment is complete with a tergite and a sternite, though the former is usually concealed under the carapace and becomes exposed only occasionally, when the abdomen and the cephalothorax are disrupted or at least fully stretched. The number of abdominal segments is fixed, ten in one of the Orders, eleven in the other. Anus with an operculum. Respiration by means of two or three pairs of book-lungs, dependent upon the Order. The separation of the Orders is simple, as indicated in the key. Both Orders are extinct, found only in the Palaeozoic. Introductory Remarks. 6. Order HAPTODA This Order of fossil Arachnida was established by Pocock in 1911, when he proposed it for the inclusion of a single species, Plesiosiro madeleyi, found in the Upper Carboniferous Coal Measures at Coseley, near Dudley, England, in a bed of nodular ironstone about ten feet above the "ten yard" coal. It was established primarily on the basis of segmentation of the first tarsi, for Pocock was not acquainted with the other characters peculiar to this Order. From his statements it is not quite clear how many specimens he had at his disposal. There must have been at least five, because Pocock mentions besides the type in the "collection of the late Mr. William Madeley," "other specimens in Mr. Madeley's, Dr. Hind's, Mr. Priest's, and Mr. Egginton's Collections." (p. 44.) None of these specimens was com plete. The type, according to Pocock, "shows the basal segments of the mandibles, the two palpi, one complete leg of the first pair, the femur, patella, and half the tibia of the third leg, the femur and patella of the fourth, and the femur of the second; the shape of the carapace and the tergal plates of the opisthosoma. Also the posterior sterna of the opisthosoma; and the hollow spaces of the basal seg. ments of the legs of the first pair." (p. 44.) The other specimens studied by Pocock "show additional features which made it possible to restore the dorsal surface tolerably completely. Details of the ventral surface are in no instance well preserved." (p. 44.) Thus Pocock's description of the characters of the species was, of necessity, based on a comparative study of several specimens, on the assumption that they belonged all to the same species. That such an assumption is not always safe, is demonstrated by the fact that of his four paratypes the one of the Wheelton Hind Collection now belonging to the British Museum and sent to me for study, after having been subjected to careful cleaning proved to be not a Plesiosiro at all, but a member of the quite remote Order Phrynichida, presumably a Graeophonus anglicus (q.v.). However, the other three paratypes undoubtedly belong to the same species as the type. Unfortunately, the specimens were not sufficiently cleaned and the structures were not adequately exposed to view at the time when Pocock studied them. This circumstance was responsible for the fact that some of his statements are not correct. Still it remains to his eternal credit that he sensed the existence of a distinct type of an Arachnid and created for it a new Order. The strict rules of the British Museum made it impossible for me to examine and study the type. But I have had the privilege of handling all of Pocock's paratypes. After cleaning them of the white mineral obstructing the view of the true surface of the specimens, the tarsus of the first leg in the paratype In. 22835 and the tarsi of the third and fourth legs in the paratype |