66 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Carboniferous. Its color is grayish yellow, not unlike that of Campodus 
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? 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. davisit, 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 Hdestus 
davisit, 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 
1 It is evident that C. lecontet belongs in the neighborhood of C. annectans 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, they 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 Hdestus 
minor is preserved in the Cabinet of Amherst College, and that of KH. heinrichi in 
the Illinois State University at Urbana. 
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