BEDS or THE PEKMIAN EPOCH IN NORTH AMERICA. 295 



These specimens show that the species I named Edaiihosaurus microdus* must be 

 placed in I^aosaarus, where it represents the second species with transverse processes 

 on the dorsal neural spines. The teeth of the palatine patch in this species are larger 

 and more closely i)laced than in the D. cruciger. The distinction between the two 

 species in the form of the apices of the neural spines, to which I referred in my descrip- 

 tion (1. c.) holds good ; but the N. clavif)er has them dilated antei-oposteriorly nearly 

 as in the D. inicrodiis. 



Vertebne. — A large series of these is preserved, and they show many interesting 

 characters. The intercentra are not distinct in the anterior part of the column, but 

 are separated posteriorly and in the sacrum. The centra are compressed and have 

 an acute inferioi* heel. The neural spines are moderately compressed below the first 

 transverse processes ; above this point they are antei'opostei'iorly oval in section. The 

 distal half is compressed. They expand to a point below the apex, where the antei'ior 

 edge extends obliquely backwards to the summit. A short corresponding oblique 

 edge truncates the posterior superior angle. The medullary cavity of the spine is 

 not closed at the apex. On several of the vertebras the lowest transverse process is 

 double, but the sides of the same vertebra differ from each other in this respect in some 

 instances. 



The two sacral vertebras are not coossilied, and the zygapophyses are well de- 

 veloped and distinct, as are the intercentra. The latter are flat, and but little 

 developed in the upward direction. The neural spines are rather elevated and slen- 

 der. They are compressed without cross-pi'ocesses, and the apex of the spine has 

 small tubercles. 



JRibs. — The ribs ai'c long and well curved, and are moderately compressed on 

 their proximal half, and cylindric for their distal. The head is w^ell distinguished 

 from the tubercle as in the manner of a mammal. That is, the tubercular surface 

 is sessile on the convexity of the rib, and not licdunculate. In this respect these ribs 

 diffei" from the usual form of two-headed reptilian ribs. The head is so long on the 

 anterior dorsal vertebra", as to articulate with the posterior edge of the vertebra in 

 front of the one with which its tubercle articulates. It becomes shorter on the pos- 

 terior parts of the column, articulating with the edge of the rib which supports the 

 tubercle. On the caudal sei'ies the head is reti-acted so as to be close to the tuber- 

 cular articulation, \yhich is the most extensive, and which is deeply notched on one of 

 its faces. This gives the appearance of a three-headed rib in this genus and in Dime- 

 trodon. 



* Proc. Amer. Pliilos. Soc, 1884, p. 37. 



