260 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



specimen, which is now the property of the Walker Museum (Cat. No. 

 10038). 



To the mmd of the present writer the conclusion is irresistible that 

 the anterior and posterior plates present m the right and left hand 

 sides of the jaw have been crowded against one another so as to he 

 in juxtaposition along the median hne as the result of post-mortem 

 deforaiation. They did not naturally form a compact pavement 

 during life, but the right and left halves were separated, leaving a 

 V-shaped area between them, as in CochUodus. This inferred separa- 

 tion thi'oughout their length would permit of the presence of a series 

 of Ilelodus-likG teeth in contact with the front margin of the anterior 

 pair of grinding plates, and it is not necessary to assume that their 

 place was taken by a single pair of small triangular teeth. In a word, 

 the evidence furnished by the type of tliis species does not appear to 

 be irreconcilable with well established reconstructions of Psephodont 

 and Cochliodont dentition. 



Genus DELTODUS Agasslz. 



A discussion of the relations between this genus and Sandalodus 

 was pubhshed by E. B. Branson a decade ago, in an article entitled 

 Notes on Carboniferous Cochliodonts.^ We are not able to share this 

 author's view that only a single dental plate is present on each side 

 of the jaw above and below in Saridalodus instead of three, as in Del- 

 todus and most Cochhodonts. Again, in his discussion of the teeth 

 commonly known as Deltodus occidentalism he undertakes to remove 

 this species to Sandalodus, "because there is evidently only one tooth 

 to each ramus of the jaw." This latter statement is merely an as- 

 sumption restuig upon negative evidence, and no proof has yet been 

 adduced to show that the number of dental elements present in the 

 mouth of Sandalodus was the same as in Deltodus. 



DELTODUS OCCroENTALIS (Leidy). 



Plate 8, fig. 3. 

 CochUodus ocddentalis Leidy, Trans. Amer. Philos. Soc, vol. 11, 1857, p. 88, pi. 5, 



'figs. 3-16. 

 Deltodus ocddentalis Eastman, Bull. Mus. Comp. Zool., vol. 39, 1902, p. 200, pi. 4, 



fig. 38; pi. 5, fig. 53. 

 Sandalodus ocddentalis Branson, Joum. Geol., vol. 13, 1905, p. 27, pi. 1, figs. 



8 9 



Sandalodus ocddentalis Branson, 30tli Ann. Kept. Dept. Geol. Nat. Resources 



Indiana, 1906, p. 1384, pi. 41, fig. 33. 



The complete synonymy of this species is given in the above-cited 



articles by E. B. Branson and the present writer. In our opinion, 



however, Doctor Branson is in error in transferring the species to the 



J Journ. Geol., vol. 13, 1905, pp. 25-27. 



