TRIONYCHID. sil 
The living species included by the present writer under this genus are those embraced 
under the heads 1, A and 1, B, 2 and 3, of Dr. Boulenger’s synopsis of species, on page 244 of 
his Catalogue of Chelonians. The type of the genus is Trionyx euphraticus of the same work. 
It is possible that Trionyx subplanus Geoffr. ought to be regarded as the type of the genus 
Dogania. Besides the fossil North American species whose remains are complete enough to 
prove that they belong under the present genus, a considerable number of others are placed 
here provisionally. 
For a discussion of the name A myda see Stejneger, Science, XXI, 1905, page 228. 
As remarkt under the genus 4s pideretes it seems most probable that the upper Cretaceous 
species placed here under Amyda really belong under As pideretes. 
Key to NortH AMERICAN SPECIES OF AMYDA. 
A‘. Upper Cretaceous species: 
1. Sculpture coarse, mostly of circular pits, about 4 in line of 16 mm.............. prisca 
2. Sculpture still coarser; 3 pits in line 15 mm. long; pits deep, rising gradually to 
summit of wall....... : Pan ate ie Bia ad bray Sung eat) aidt eco: phi aha ae Bie Glia gs eh@y Bldaaieaee! a halophila 
A*. Species of Atlantic slope Eocene: 
1. Middle of costal with irregular pits, the sutural borders with ridges somewhat 
oblique to the borders; about 2 ridges in a 10 mm. line.................... pennata 
2. Costals much thicker than in pennata; pits and ridges coarse as in pennata 
but irregular or in rows at right angles with the sutural borders............. virginiana 
A*. Wasatch species: 
1. Costals thick and growing thicker toward outer end; sculpture coarse; irregu- 
larly arranged and deeply imprest pits; 4 or 5 in line 20 mm. long........... cartosa 
2. Costals thick; sculpture mostly of winding and anastomosing ridges inclosing 
pits and short furrows; 2 or 3 ridges crost by line'of §: MMs... 3. ic os esas ventricosa 
3. Costal bones thinner than in cariosa; the sculpture similar................-. radula 
A‘. Bridger species: 
1. Carapace nearly as wide as long; front of nuchal long and nearly straight; with 
a smooth band infront; 5 or OV pits im) 20MM. . 0h. cos. ees ct ems eres aqua 
2. Carapace nearly as broad as long; 4 to 7 pits, usually 5, in 20 mm. line; no 
depression along back; nuchal, from side to side, 0.64 the width of the shell... wintaénsis 
3. Carapace nearly as wide as long; a conspicuous depression along the back; length 
of nuchal 0.80 of width of shell; with a smooth band in front........... Scutumantiquum 
4. Costal bones thin; on proximal ends of costals, 2 pits in 10 mm.; on distal ends, 
3 or 4; some ridges crossing the costals more conspicuous than others........ concentrica 
5. Carapace nearly as broad as long; nuchal not half as wide as carapace; sculp- 
ture‘of median coarseness, 3 pitsim TO MM... oi. cia eG os eee eee cases francisce 
6. Carapace broader than long; nuchal nearly 0.6 the width of the carapace; 
sculpture coarse and irregular, on central portions from 2 to 5 pits in 20 mm. salebrosa 
7. Carapace about as broad as long; the bones thin; nuchal concave in front, its 
length nearly 0.7 the width of the carapace; a smooth band along its fronts 
Sculpture coarse, abouts) pits) imlOr mii ING, sise n.te stele feta gs cet ete exquisita 
8. Carapace nearly as broad as long; rounded in front and behind; nuchal a little 
more than half the width of the carapace; on proximal ends of costals, 3 pits 
in 15 mm., on neurals and on distal ends of costals 5 or 6 pits in 15 mm. line. . mira 
g. Known only from skull, which resembles that of 4. ferox; crushing surfaces of 
upper jaw broad..... : tritor 
to. Carapace nearly as broad as long; auéhall not one-half thie width ofthe carapace; 
sculpture coarse, 3 or 4 pits in 20° mms TIN. .aics os cee se eee e ewes vee ee: egregia 
A°. Uinta species: 
1. Carapace broadly oval; nuchal 0.65 the width of the carapace; sculpture coarse, 
MOK 2) IES MUTI LORIE Me Mit ctere: ees Reps etcatiayshao spatena acaVereraseusesiesstslginegs Soars erecta =< crassa 
A®, Miocene species: 
1. Costals thick and heavy; crost by narrow, sharp ridges, like those of a fle, 
Omiya DOUGs INI cals eayeateasss stew cla tee oe wits: oS elelsiele weelece le Metis ei? sald us aes + lima 
2. Costals not so thick; ridges closer together than in/1ma and curving across costal butet 
3. Pits of costals closely placed, irregular in size and remarkably deep...........- cellulosa 
