—— 
———— 
TRIONYCHID. 507 
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 4. guttatus (Leidy). From the latter it differs in being 
more elongated, the width being coneained’s in the length seventy-six hundredths times, in A. 
guttatus, eighty- -five hundredths times. The sculpture of A. ellipticus i is coarser, there being 
4 or § pits in a 20 mm. line, while in 4. guttatus there are 5 or 6 pits in the same distance. 
The bridge of the plastron of ell: pticus is wider relatively to the length of the hyohypoplastral 
suture than was 4. 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 4. grangeri. The 
distinctive characters are discust under the latter species. 
Aspideretes grangeri sp. nov. 
Plate 97, fig. 1; 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. t. 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*; that is, the upper portion of the 
middle Bridger. 
The total length of the carapace (plate 97, fig. 1; text-hg. 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. Asin J. ell pticus, the upper 
layer of the carapace overhangs Sore hat the middle layer, so that a sort of gutter runs 
around the edge of most of che’ carapace. The free border of the fifth costal plate i is 7mm. 
thick near the suture, and 11 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 4. ell: pticus, 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 toa 
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 
eM Sutt re eo al 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 
Preneural..... 26 23 of the median costals projected about 37 mm. beyond the 
| eS apt | 8 a border of the disk. 
Ae a i? ; The sculpture of this species consists, as 1s usual in the 
| Neural 3...... 44 27 Pp if O , 
ite Aevees eal 26 family, of a network of ridges surrounding shallow pits. 
| Neural 5..... 38 2 “ : : ‘ 
eeteeabee > 4 The ridges are rounded on their summits. On the outer 
| Neural. 65. ..<... | 29 15 
| | 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 GE 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 ina line of the length given. Most of the costals have a narrow 
smooth band along the intercostal sutures. 
