66 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Carboniferous. Its color is grayish yellow, not unlike that of Campodua 

 and other fossils from the Missourian series of this country ; but on 

 the other hand the individual teeth undeniably approach Helicoprion in 

 form, and hence are suggestive of a corresponding horizon. 



Why, then, if the teeth are of similar form, should not the specimen 

 be referred directly to Helicoprion 1 The answer is that such a course 

 would be objectionable for several reasons. In the first place the com- 

 plete symphysial dentition of the latter genus consists of approximately 

 three and one-half whorls, the largest known example measuring 26 cm. 

 in diameter, and comprising upwards of 150 teeth. There is no evidence 

 to show that the present series of twenty or more teeth was ever coiled 

 into a complete spiral, any more than was the case with C. davisii, for 

 instance ; and certainly no marks of contact with a preceding inner 

 whorl are visible along the base. Secondly, the occurrence of irregular 

 patches of enamel-covered dentine along the base of the series recalls 

 conditions we have already become familiar with in Campodus, and sug- 

 gests that the arch was supported directly by cartilage as in that genus, 

 and not spirally inrolled. Furthermore, if we assume this to be only a 

 fragment of a complete volution, and that the inner whorls have been 

 broken away, we shall find on continuing the indicated curvature that 

 the diameter of the complete spiral exceeds that of the largest known 

 example of Helicoprion, while at the same time the individual teeth are 

 proportionally smaller, which is contrary to what we should expect 

 them to be. This statement can be readily verified by a comparison of 

 the accompanying illustration with the figures given by Karpinsky, espec- 

 ially text-figure no. 47, opposite page 426 of his memoir. And finally, 

 we note there are no lateral grooves extending along the series near the 

 base, as in the Russian genus. There would thus appear to be ample jus- 

 tification for placing the present example, and also the type of £destus 

 davisii, which was included by Karpinsky with Helicoprion, in a separate 

 genus as we have done. ^ 



It is to be regretted that the fossil under discussion should have been 



■^to' 



1 It is evident that C. lecontei belongs in the neigliborhood of C. annednns and C. 

 davisii, rather than with Edestus, owing to its more strongly arched condition and 

 greater number of segments. Although the form of the anterior teeth is obscured 

 by faulty preservation, tiiey apparently had the same general configuration as the 

 rest, and the base is longitudinally channelled. For an opportunity to examine the 

 type-specimen of the Nevada form, the writer is indebted to the kindness of his 

 friend, Dr. J. C. Merriam, of California State University. The type of Edestus 

 minor is preserved in the Cabinet of Amherst College, and that of E. heinrichi in 

 the Illinois State University at Urbana. 



