Makyland Geological Survey 203 



In the collection of Goucher College are two more teeth, one (No. 

 2604) referable without question to Astrodon, differing from the type 

 only in the degree of wear, which has involved not only the apex and the 

 margin on either side, but the greater part of the surface of the crown, 

 so that the characteristic wrinkled aspect is only discernible over a portion 

 toward the fang. 



The other specimen (No. 3333) (pi. xix, jfig. 4), while nearly as large as 

 the tooth just mentioned, differs from both it and the type in lacking the 

 spoon-shaped curvature characteristic of the others; in fact, it is strik- 

 ingly like many other teeth in the collections referable to PUuroccdus 

 nanus, except that it is about twice the size of the average of the latter, 

 or about as much larger as the tibia of Fleurocalus alius Marsh (vide 

 supra) exceeds that of P. nanus. Moreover, among the number of 

 teeth referable to P. nanus there is a considerable range of variation 

 in shape, though no very great difference in size; some of them re- 

 sembling very closely the type tooth of Astrodon johnstoni except for 

 size. 



Hatcher ^ has already called attention to this similarity, but made no 

 mention of the great disparity of size, a point brought out by Lucas." 

 I am inclined to agree with Hatcher in considering Astrodon and Pleu- 

 roccelus synonymous, but not in the synonymy of the species P. nanus 

 with Astrodon johnstoni; for, in spite of the fact that the vertebrg3 of 

 Pleurocoelus nanus, referable to this species, are without exception those 

 of immature animals, they, together with foot and limb bones of appro- 

 priate size, as Lucas says, " greatly outnumber all the other vertebrate 

 remains obtained from the vicinity of Muirkirk, Md.^' This is also true 

 of the teeth referred to this species. Pleurocoelus altus, on the other 

 hand, is represented by but few bones, and could readily have been the 

 , possessor of teeth like those of Astrodon johnstoni as well as of the two 

 specimens mentioned in this section. It is therefore quite possible that 

 Pleurocoelus altus should be considered as synonymous with Astrodon 

 johnstoni, in which case the latter name would take precedence. It 



^ Hatcher, Ann. Carnegie Mus., vol. ii, 1903, pp. 12-14. 

 ^ Lucas, Science (N. S.), vol. xix, 1904, p. 436. 



