TRIONYCHID^:. 



57 



No. 5930. The outer anterior process was evidently flattened, not terete as usual in trionychids. 

 The pits and ridges of the median end are quite distinctly seen. The width of the bone where 

 narrowest is 53 mm. 



The species resembles most closely A . guttatus (Leidy). From the latter it differs in being 

 more elongated, the width being contained in the length seventy-six hundredths times, in A. 

 guttatus, eighty-five hundredths times. The sculpture of A . ellipticus is coarser, there being 

 4 or 5 pits in a 20 mm. line, while in A. guttatus there are 5 or 6 pits in the same distance. 

 The bridge of the plastron of ellipticus is wider relatively to the length of the hyohypoplastral 

 suture than was A. guttatus. A. guttatus has fontanels in the front of the carapace; while 

 A. ellipticus has none. 



This species resembles closely the form described in this work as A. grangeri. The 

 distinctive characters are discust under the latter species. 



Aspideretes grangeri sp. nov. 

 Plate 97, fig. i; text-fig. 667. 



Among the fossils collected by Mr. Walter Granger, head of the American Museum 

 expedition to the Bridger beds in 1904, was the fine carapace represented on plate 97, 

 fig. I. Only a portion of the middle region at the rear is missing. The specimen bears 

 the catalog number 3942. It was collected on Cottonwood Creek, about half a mile below 

 the Henry's Fork stage road. The level is given as B 3 ; that is, the upper portion of the 

 middle Bridger. 



The total length of the carapace (plate 97, fig. I; text-fig. 667) was 383 mm.; the width 

 of the disk, 317 mm.; the width to the free ends of the ribs, 343 mm. The carapace is con- 

 siderably archt from side to side, the midline of the fossil rising to a height of 105 mm. above 

 the tips of the free rib ends. In outline the carapace is broadly oval, or elliptical, slightly 

 excavated in front, and probably slightly truncated in the rear. As in A. ellipticus, the upper 

 layer of the carapace overhangs somewhat the middle layer, so that a sort of gutter runs 

 around the edge of most of the carapace. The free border of the fifth costal plate is 7 mm. 

 thick near the suture, and 1 1 mm. thick thru the rib. The nuchal has an extent from side to 

 side of 190 mm.; a fore-and-aft extent of 40 mm. As in A . ellipticus, there is a smooth band 

 along the front and the ends of the nuchal. It runs at a lower level than the pitted surface. 

 It is about 7 mm. wide at the midline, and 23 mm. at the ends of the bone. 



There are a preneural and 6 neurals. Possibly there was a seventh neural of small size. 

 The table below gives the dimensions of these bones. 



At their proximal ends the costals of the first pair have a width of 59 mm. At the distal 

 end they are only 39 mm. The next four have the proximal ends equal in width to the lengths 

 of their respective neurals. The distal end of the costals of the second pair is expanded to a 

 width of 88 mm. This may be an individual variation. The costals of the sixth pair probably 



joined each other for a part of their width at the proximal 

 ends. Those of the next two pairs certainly joined their 

 fellows at the midline. The lateral extent of each costal of 

 the eighth pair was close to 36 mm. The free ends of the ribs 

 of the median costals projected about 37 mm. beyond the 

 border of the disk. 



The sculpture of this species consists, as is usual in the 

 family, of a network of ridges surrounding shallow pits. 

 The ridges are rounded on their summits. On the outer 

 third of most of the costals the pits are arranged in rows 

 running parallel with the adjacent border of the carapace. 

 On the nuchal, the neurals, the costals of the first pair, and the proximal two-thirds of the 

 other costals, the pits are irregularly but evenly distributed. On the greater part of the cara- 

 pace there are 5 or 6 of the pits in a line 20 mm. long. On the anterior third of the carapace 

 there may be as many as 7 in a line of the length given. Most of the costals have a narrow 

 smooth band along the intercostal sutures. 



