AND AYES OF NORTH AMERICA. 



137 



The third and fourth' marginal bones, while of the same length as tho3e of 0. emarginatus, are half as wide 

 again, a form produced by the projection inwards of the lower face, The fifth presents the same peculiarity in a 

 more marked degree, and has a thicker outer margin or is more rounded from below. The fossa, for the rib is less 

 than .2 the length of the bone, while the same in (>. emarginatus is .33 the length. The seventh marginal has the 

 prominent inner lower edge, but is more elevated than the same in the species last described. Its superior surface 

 is therefore considerably more concave. The, most, posterior marginals, as characteristic of the genus, are prolonged 

 considerably ■within the inner suture of the marginal scuta,. They are quite flat, plane above, and with a rounded 

 concavity beneath within the margin; the rib pit is flattened in these. The dermal suture crosses the marginal hones 

 in all the marginals from the fifth backwards inclusive just in front of the costal pit. A hyosternal, a hyposternal, 

 and (wo xiphisternal bones are all that remain of the sternum. They are of much the same form as those of 0. 

 emarginatus. Tin; hyposternal has the external groove posteriorly to receive the xiphisternal, while the episternals 

 have a, groove internally to receive the hyosternals. The xiphisternal are toothed on their inner margin for common 

 suture which is not, so long as in o. emarginatus. The xiphisternal have evidently been shorter and more broadly 

 rounded behind than in that species. They have not, tin; same thin acute external margin proximally nor strong 

 intermarginal thickening distally seen in the same, but are of more uniform proportions. The hyosternal preserved 

 is 1,1k; distal portion, while thai, of 0. emarginatus is chiefly proximal. It is however obviously a, thinner plate than in 

 the latter, and more as in Propleura sopita. The anterior margin preserved is that between the, episternal an 1 

 axillary portions; it is regularly thinned out; the distal part of the bone is flat, and the median suture toothed. A 

 short free margin indicates a mesosterual fontanelle. Median and posterior fontanelles also present,. 



Measurements, 

 Length second marginal, 

 Width " " (external) 



Length fifth " 



Width " " (below) 



Length seventh " 



Width " " (below) 



Length tenth " 



Width " " (external) 



Length of a, vertebral bone, 



Width " 



from end of xiphisternal notch to anterior margin of hyposternal, 



Greatest width episternal, 



In. 



Lin. 

 0.7 

 4. 

 11. 



o 



S. 



o 



:'.. 



w 



to.:, 



2 



5. 



1 



9.5 



o 



(i. 



3 



4..> 



Portions of another individual from Barnesboro, confirm the characters already given, and indicate the largest 

 Of the group known by the shell alone. 



The remains are the first and eleventh marginal bones of the right side, and the fifth of the left, with the nuchal 

 and numerous costals, including the humeral or first costal. Also several vertebral hones, with parts of the sternum, 

 the scapula, COraCOid, femora, etc. 



The marginals exhibit the characters of the genus, the eleventh particularly, which is wanting in the first 

 specimen, exhibiting asuture for union with pygal bono. It is therefore produced much beyond the suture, of the 

 marginal scuta,, a peculiarity not, existing in any species of Propleura. The same, hone is relatively considerably 

 stonier than in I'. sopita,. The first marginal is deeper and shorter than in the same, and the fifth differs in the same 

 way. anil is much w ider as w ell. The nuchal is concave and arched medially, and bears a well marked marginal 

 scutum. The adjacent scutum on each side is relatively shorter than any of the others, and has an' oblique inner 

 suture. 



The vertebral hones are narrower than in the (). platylomus and are elongate oval in outline behind. They 

 present superiorly a- shallow longitudinal groove interrupted at, the middle of the length. 



Tim scapula, presents a, short coraeoid articular surface. The procoracoid is flattened in the plane of the scapula. 



AMERI. PHILOSO. SOC. VOL. XIV. 35 



