PLASTOMENID&. 467 
especially struck by the configuration of the inner end of the hyoplastral bone, which appeared 
to him greatly different from that of Trzonyx,; but he does not mention the condition of the 
median and hinder portions of the plastron. 
In 1877 (Wheeler’s Sury. rooth Merid., 1v, p. 47), Cope concluded that the hyoplastrals 
were not greatly different from those of Te while the hypoplastrals were materially 
different. ee are stated to have displayed a transverse width behind the inguinal region 
more like an emydoid than a trionychoid genus. The more extended ossification of all these 
bones in Plastomenus than in other genera of trionychids was recognized. Cope’s remarks 
on the genus in the work referred to were copied into his work of 1884: on the vertebrates of the 
Tertiary formations. 
Even as late as the year 1882 (Amer. Naturalist, xvi, 991) Professor Cope was uncertain 
whether or not this genus belonged to the Emydidz. 
Several of the species referred to this genus are based on very fragmentary and incomplete 
materials, and it is not improbable that ravtien more complete remains shall have been dis- 
covered some of these species will have to be placed in other genera. 
ANALYSIS OF SPECIES REFERRED TO PLASTOMENUS. 
A‘. Judith River and Laramie species: 
1. Costals with angular pits, 5 in 10 mm., and crost by prominent welts. costatus 
A*, Arapahoe species: 
2. Costals without welts; pits fine, not angular, 6 in 10 mm punctulatus 
3. Costals not known; free border of hypoplastron acute; lower surface with 
angular pits . ; - insignis 
A*, Puerco or Torrejon species: 
4. Carapace with welts. Carapace and plastron with small pits............... acupictus 
A‘. Wasatch species: 
5. Like P. thomas, but ridges between pits broader; 7 pits in a line 15 mm. long catenatus 
6. Costals thick; pits on distal ends of costals in rows; 3 or 4 pitsinaline of 10 mm. — /eptomitus 
7. Costals thick; sculptured with pits and welts; pits circular, 7 on 10 mm.......  lachrymalrs 
8. Costals of moderate thickness, pits angular, 7 in 10 mm; some of the intervening 
ridges weltlike ......... ; Se Tne kaa oes en ee 5 AS fractus 
g. Pits of costals abruptly sunken: 5 in 10mm.; no welts ; _plastron with ver- 
miculate ridges. ... : : sae fe corrugatus 
10. Costals thick; pits circular, 4 in 10 mm. n.; oblique welts on some costals; plastron 
with rows of circular pits . . fork sean communis 
A®. Bridger species: 
i. Carapace with welts and pits; four ian ina 10 mm. line. Costals of eighth 
pair as long as wide.......... Bae oft Pie nates chit Mein te hry evan aint nial thomast 
12. Carapace with welts and pits; five: or siX pits in 10mm.; eighth costals much 
shorter than broad ; visendus 
13. Carapace with welts and pits; eight pits in 10 mm.; hinder cost. ils about as 
NST Seta Sew Cae, Meme re onset ene oe telat asic SB celal a cence ORs ; ; tantillus 
14. Carapace with welts on hinder ae igaree or fous pits in 1omm..... @demuius 
15. Like edemius but with from five to seven pits in 10 mm..... molo pinus 
Plastomenus costatus Cope. 
Plate 85, figs. 1, 2. 
Plastomenus costatus, Copx, Vert. Cret. Form. West, 1875, pp. 94, 261, plate viii, fig. 8; Proc. Acad. 
Nat. Sci. Phila. 1875, p. 9; Brit. N. A., Bound. Comm. Report on Geol. etc., 1875, p. 337.—Hay, 
Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 452.—Harcuer, Bull. U.S. Geol. Surv. No. 257, p. 74. 
This species was described from materials collected by Dr. G. M. Dawson, south of Wood 
Mountain, Assiniboia. The deposits from which they were derived were supposed to belong 
to the Laramie, but are now known to belong to the Judith River. These materials are now 
the property of the Geological Survey of Canada. They consist of a piece of a costal, a frag- 
ment of probably the right hypoplastron, and another small undetermined fragment. The 
costal fragment was figured by Cope as cited. The bone is remarkable for the relative thick- 
