XIII. A NEW SPECIES OF HELODUS. 



By Charles R. Eastman. 



Helodus comptus, sp. nov. 



Description. — Teeth of moderate size, laterally elongated, having 

 the coronal contour gently arched without rising into a distinct promi- 

 nence, and the general surface wrinkled by a numerous series of fine 

 transverse corrugations which extend over the entire superficies between 

 the long lateral margins without being interrupted by a longitudinal 

 crest. Punctations of the coronal surface confined to and apparently 

 determining the linear arrangement of the transverse rugae. The 

 root is apparently short, reaching but little below a narrow smooth 

 band at coronal base along the lateral margins, and coarsely crenulated 

 as in some species of Chomatodus . Transverse rugae becoming more 

 or less obliterated in worn specimens, and punctse appearing as rather 

 conspicuous pores. 



The above definition is intended to express the more salient charac- 

 teristics of a number of detached Cochliodont teeth from the 

 Waverly of northern Pennsylvania, recently submitted to the writer 

 for investigation by Mr. William Millward of Meadville. Although the 

 generic relations of these anterior teeth are necessarily somewhat un- 

 certain, there can be no doubt that they are specifically distinct from 

 all forms of Cochliodont dentition hitherto described, and consider- 

 able interest centers, therefore, in their discovery. The majority of 

 dental crowns are well preserved, the roots imperfectly so. They 

 present little individual variation, but show among themselves differ- 

 ent effects of wear. The largest specimen in the collection has a total 

 length of slightly less than 2 cm., and breath of 0.7 cm. In smaller 

 specimens the dental crown is proportionally somewhat wider. 



Different types of the anterior dentition of Cochliodont sharks are 

 commonly assigned to various genera whose status must be regarded 

 as purely provisional : such, for instance, as Helodus (exclusive oi H. 

 simp/ex), Chomatodus, Lophodus, Venustodus, in which the lenticular 

 crowns cannot be correlated with the large posterior grinding plates 

 of well recognized forms. It happens, moreover, that the anterior 



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