AND AYES OF NORTH AMERICA. 



143 



C ATA PLEURA, Cope. 



Tn this genus, as in the two preceding, the earapacial disc is united by suture to two 

 marginal hones, on each side of the nuchal bone, forming a solid arch. What the mode 

 of attachment between the two may be posteriorly, material is not sufficient to deter- 

 mine; but from the form of some tenth and ninth marginals, I. suspect that this union is 

 not so great as in Osteopygis, but rather as in Propleura, by the caudal marginal only. 

 There is a nuchal scutum, as in the last genus. What distinguishes it from that genus, as 

 well as from Osteopygis, is the entire absence of the rib and pit articulation between the 

 second marginal and the corresponding costal bones. It is in this respsct similar to Che- 

 lyd ra, and to Chelone, counting one rib less than in Propleura. From the similarity in 

 thickness and form of the first marginal, 1 suppose the genus Lytolomato have been simi- 

 lar to the present, in this respect, and a supposed second marginal confirms the view. 



The only species of this genus yet known is peculiar in the form of the nuchal margi- 

 nal. It is not wider than the first and second marginals, and does not, therefore, extend 

 over the front of the carapace, as in Osteopygis, Chelydra and Chelone. It is intermedi- 

 ate in extent in Propleura sopita, while it is identical in form in the Lytoloma jeanesii. 

 The natural position of the type species is, therefore, plain enough. In the present genus 

 and Propleura the form of this piece is perhaps of not more than specific value. 



I. The margins of the posterior marginal plates repand or concave. 



Posterior lateral hones, with upper margin produced within, narrow ; width 6-7ths 

 length, margin, openly repand ; anterior marginal scuta, 2% long as wide, many of these 

 bones confluent with disc, none concave on outer surface. 



C. REl'ANDA. 



«! ' 



CATAPLEURA REPANDA, Cope. 



Osteopygis repandua, Cope, Proo. A. N. Sri., Phila., L86S, p. I 17. 



This species is bused on remains of one individual, which is represented by parts or wholes of ten marginal and 

 of many costal plates, lis size, is smaller than the preceding species, and it is further characterized by the repand 

 outline of the posterior marginals with obtuse points at the dermal sutures. The middle marginals are concave in- 

 stead of convex below, as in 0. emarginatus. The narrow anterior marginals are convex on the outer surface, and 

 bear very elongate scutes, which are narrower than in any other species. Five of these marginal bones have been 

 united above by suture to vertebral or costal plates, indicating the same degree of ossification as in 0. e margin a- 

 t u s . The dermal sul ures are less marked than in that species, but are indistinct, as in P. sopita. On two coi tal 

 plates, the margins of these are distinot. They are straight, make open angles with the transverse grooves, and with 

 each other, and indicate scutes longer than broad. The costal bones are plane, longitudinally, but considerably de- 

 curved from and below the middle. The costal ridgo is distinct throughout, and narrow, and extends obliquely to 

 the posterior suture, and then projects shortly for attachment to the marginal bone. The costal beads present at their 

 posterior bases an acute ridge, which diverges posteriorly, embracing a strong groove between it and the body of the rib: 

 both extend but a short distance posteriorly. 1 have not seen this feature in the ribs of the 0. emarginatus, and 0. 

 platylomus. 



