TRIONYCHID^. 503 



Aspideretes? guttatus (Leidy). 

 Text-figs. 663, 664. 



Trionyx guttatus, LEIDY, Proc. Acad. Nat. Sci. Phila. 1869, p. 66; U. S. Geol. Surv. Wyoming, etc., 

 2d (4th) Ann. Kept. F. V. Hayden, 1871, p. 367; U. S. Geol. Surv. Montana, etc., 5th Ann. Rept., 

 F. V. Hayden, 1872, p. 370; Cont. Ext. Vert. Fauna West. Terrs., 1873, pp. 176, 342, plate ix, 

 fig. I. COPE, Ext. Bat., Rept., and Aves N. A., 1869, pp. 151, 152; U. S. Geol. Surv. Terrs., 

 6th Ann. Rept. F. V. Hayden, 1873, p. 617; Vert. Tert. Form. West, 1884, p. 119. HAY, Bibliog. 

 and Cat. Foss. Vert. N. A., 1902, p. 454. 



Aspideretes? guttatus, HAY, Amer. Geologist, xxxv, 1905, p. 335. 



Dr. Joseph Leidy's type of this species was discovered at Church Buttes, near Fort Bndger, 

 Wyoming, in the beds of the Bridger Eocene. It consists of a portion of the third neural plate, 

 the fourth, fifth, sixth, and seventh neurals; portions of the third, fourth, fifth, and sixth 

 costals of the right side; the proximal ends of the fifth, sixth, seventh, and eighth costals 

 of the left side; and the complete seventh and eighth costals of the right side. The materials 

 are therefore not very satisfactory. The form of the shell can not be determined, nor with 

 certainty the presence or the absence of a preneural. The species has here been referred with 

 doubt to Aspideretes. To add to our difficulties the type appears to have disappeared from 

 view. Cope referred to this species some of the materials collected by him in the Bridger beds, 

 but his specimens were very fragmentary and do not appear to have furnisht him with ad- 

 ditional information. It is questionable whether or not the nearly complete carapace collected 

 by him in the Wasatch beds of New Mexico really belongs to the species. Unfortunately this 

 carapace is now lost, along with the greater part of Cope's other remains from that region. 



Leidy supposed that the carapace described by him had originally had a length of about 

 375 mm. The bones had a thickness of about 8 mm. Most of the neurals are nearly twice as 

 long as wide, and there is a reduced one between the costals of the seventh pair. The costals 

 and neurals are described as being sculptured for the most part with broad, rounded, and 

 isolated concave pits resembling the impression of rain drops on a soft surface. Near the bor- 

 ders of the shell these become somewhat confluent. The walls surrounding the pits are broad 

 and low and often as wide as the pits. There are 2.5 or 3 of these pits in a line 10 mm. long. 



The American Museum expedition of 1903, sent into the Bridger region near Fort Bridger, 

 secured, in the Grizzly Buttes, a specimen, No. 6005, which is referred with confidence to 

 this species. It consists of a portion of the carapace corresponding nearly with that of the type, 

 together with a large portion of the plastron. The fragment of the carapace agrees in all 

 essential respects with the figure and description furnisht by Leidy. However, the sixth 

 neural plate is segmented into two portions. The costals appear to have been somewhat 

 thicker, ranging from 7 mm. to 10 mm. The distance from the hinder border of the eighth 

 costal to the anterior border of the sixth is 1 12 mm. In Leidy's specimen this distance, accord- 

 ing to his figure, was 133 mm. Fig. 6630 is composite, being constructed partly from the 

 specimen just described and partly from No. 5993 A. M. N. H., described below. 



The plastron (fig. 6636) is represented by nearly the whole of the right hyoplastron and a 

 fragment of the left; the whole of the right hypoplastron and a fragment of the left; and both 

 nearly complete xiphiplastra. At its median end the border of the hypoplastron is filled out to 

 the extremity of the process which meets that of the opposite bone at the midline, thus 

 indicating an old individual. The bones are thick and heavy. On the bridge, at the suture 

 between the hyoplastron and the hypoplastron, the thickness is 17 mm. The bridge, where 

 narrowest, is 79 mm. wide. Of this width the hyoplastron occupies 49 mm. Nearly the 

 whole of the lower surface of both bones is roughened or granulated. However, the outer end 

 of the hypoplastron is sculptured with ridges and tubercles, of which there are about six in a 

 distance of 10 mm. A similar, but more indistinct sculpturing occupies the lower surface of 

 the outer end of the hyoplastron. 



The xiphiplastra are triangular in form, and had a fontanel between their inner borders. 

 Each has 2 processes for articulation with the corresponding hypoplastron. Two processes of 

 the left xiphiplastron received between them a single process of the right. The lower surface 

 of the two bones is roughened, but not sculptured. 



Fig. 664 represents the pelvis of this specimen. 



