35 
i 

APPENDIX B. 337 
PLASTOMENUS COALESCENS, Cope. 
This species is represented by large fragments of carapace and plastron of a 
single individual. These indicate a large animal of adult age. The fragments are 
thick, and the sutures separating the component elements have disappeared. Der- 
mal sutural grooves are also wanting. The portions of the plastron preserved are 
emydoid in character, being most thickened in the lateral portions, especially in the 
inguinal region. The borders of the carapace are free and obtuse ; at some points, 
somewhat thinned out. The ribs proper, in the portions preserved, terminate in a 
short, free extremity, shorter than in most species of Trionyz. There is no indication 
of the existence of marginal bones. 
The surface of plastron and carapace is covered with a dense layer, which is 
thrown into rather coarse, inosculating folds. These form an open, reticulate pat- 
tern towards the middle portion of the carapace, and become obscure near the 
borders. They are well marked on the plastron, and are more or less longitudinal. 
The appearance is that of a T'rionyz. 
The costal axis scarcely projects on the inner face of the carapace. The anterior 
border of the carapace is a free, thickened margin, divided by a horizontal groove. 
The presence of nuchal bone cannot be ascertained. 
Measurements. 
M. 
Thickness of the carapace at the middle of the pees of a costal bone.. Ae dine Hom Le! 
Thickness of the carapace at the anterior recat igal cise Bish csieise(e sie eae UNOS 
Thickness of the carapace at the lateral margin............0200 ccecsee cosececcce-- 0.008 
Thickness of the plastron near The Dridge.. ...... ceaccsccenecuscsceicecsacccscoess 0.015 
Mhrekness of the plastron more, Centrally: ss... 5. ones whines as <aice ceieis vle've se ouse es vie 0.000 
Four areole in 0m, 10. 
This species is found in a greenish-brown arenaceous clay deposit in the Bad 
Lands south of Woody Mountain, latitude 49°. 
PLASTOMENUS COSTATUS, Cope. 
Represented, in the collections made by Mr. Dawson, by small portions of 
plastron and carapace, which display distinct osseous, but no dermal scutal sutures. 
These specimens were discovered together, and are believed to belong to the same 
individual. The bones are thinner than corresponding ones of the two other species 
of tortoises described, from the same locality, excepting at the costal enlargement, 
which is remarkably prominent and well-defined on the under side of the carapace. 
The dense or cement layer of the carapace is thrown into very delicate, but premi- 
nent ridges, which run parallel to the axis of the carapace, and occasionally 
inosculate, or are crossed by a similar ridge running at right angles tothem. The 
sculpture of the plastron is similar, but more obtuse and obscure. The superior edge 
of the free border of one of the lobes of the plastron projects beyond the inferior, and 
is not, as is usual, less prominent than the inferior. 
Measurements. 
M. 
Thickness of a costal at the margin.. We Cina oleae caiigteasietaionay davaistnie: ss wisicies oy OOD 
Thickness of a costal at the rib.. Pata cle atic wat dns Attic c's <lc stele ageecke  OA00S 
Thickness of the free edge of the plastron.. Bir ptaatrepiedis wim ea eeigeiser aide . 0.009 
The costal bone of this species is much like that of a Trion, yx, but the character 
of the plastron refers it to Plastomenus. 
