GEOLOGICAL SURVEY OF THE TERKITOEIES. 619 



Plastomenus trionychoides, Cope. 



Anostira iiioiiychoide-s, Cope. Proceed. Amer. Pbilos. Society, lb7"i, p. IGl. (Published 



July 29.) 



The original specimen of the species was found mingled with one of 

 Anostira ornata, and being of about the same size the two were supposed 

 to pertain to a single species. I now distinguish the fragments clearly, 

 and find portions of three other individuals from other localities to per- 

 tain to the same. One of* these presents the two sternal elements de- 

 . scribed in the preceding account of P. Thomasii. 



The sculpture of the costal bones consists of reticulated ridges which 

 inclose coarser pits than in the last species, and show no tendency to 

 run into ribs extending obliquely across the bones. The second costal 

 exhibits a greatly leveled suture for the first, and its alar portion behind 

 its costal rib is twi*ce as wide as the latter. The last costal differs from 

 that of P. Thomasii in being angulate instead of truncate at the rib ex- 

 tremity, and the latter proje(its strongly beyond the angle. In the second 

 specimen the sternal bones are much more convex than in P. Thomasii 

 and more thickened inwardly. Those of the specimens from the Bad 

 Lawds of Cottonwood Creek. 



Plastohienus multifoveatus. Cope, spec. nov. 



r 



Represented by the costal bone of a specimen of much larger size than 

 the precedingand following species. Its sculi)ture is a shallow but sharply 

 iujjiressed honeycomb pitting, smaller than iu the preceding species. 

 Thus there are seventeen or eighteen pits across the middle to seven or 

 eight iir P. trionychoides. No ribs whatever. 



Measurements. 



M. 



"Width costal at middle 0240 



AVidth costal at eud 0350 



Tbiekuess at middle 0035 



Plastomenus CEDEanus, Cope. 



Anostira cedemia, Cope. Proceed. Amer. Philos. Soc, 1872, p. 461, (July 29.) 



Eepresented by most of the important parts of three specimens. These 

 all display the last and middle costals, and two of them the second cos- 

 tal s. Sternal bones are wanting, except, perhaps, in one. 



From these it appears that the anterior costals have a distantly punc- 

 tate sculpture, with rib-like swellings running diagonally across them. 

 On the middle costals the punctas disappear and the ribs grow thicker ; 

 on the last costals the ribs are broken into a number of smooth tuber- 

 cular swellings whose axes are nearly at right angles to that of the 

 carapace. The second costal has its posterior alar portion twice as 

 wide as the rib portion ; its suture with the first costal is very oblique 

 and bounded behind by a rabbet edge. The last costals are peculiar in 

 tlieir union throughout their entire length without emarginatiou for 

 pyg^l, and in the gently convex posterior outline, with projecting rib 

 end, differing in these respects markedly from P. Thomasii and P. tri- 

 onychoides. 



Measurements. 



M. 



No. 1. Length last costal, common suture 0. 045 



Length last costal, anterior 0G3 



Length last costal, exterior border 052 



Width middle costal O'JO 



Tbickuesd middle costal 004' 



