6 BULLETIN OF THE 



row extend half-way to the apex. In the eleventh row the folds are very- 

 distinct. In front the teeth are symmetrical ; those farther back have 

 lost some of the symmetry. Their bases looli as if pulled to one side 

 (backward) by the prongs. Gradually the lateral cusps become shorter, 

 until in the twelfth row they are hardly more than half as long as the 

 median. The cusps have become nearly erect and the striation is very 

 distinct in the hinder rows. Besides the keel at each side, a similar one 

 marks the front of each cusp in these rows. On these teeth the prongs 

 of the base are so short as to be scarcely noticeable, only a shallow in- 

 dentation remaining of the notch between them. Here the buttons are 

 merged in the ridges till they appear as projections on the sides of the 

 cusps, and the cusps themselves have become stouter, shorter, and more 

 like the scales. The changes appearing gradually in the lateral rows 

 have culminated in the last row, where the tooth has plicated enamel, 

 nearly straight cusps, a median cusp twice as long as the laterals, and 

 a broad rounded base without prongs or concavities and but slightly 

 notched in the posterior margin. For a description of a tooth of the 

 twelfth or thirteenth row, that of Cladodus viirabilis Ag. is not far out 

 of tlie way ; in fact, it agrees so well that, if consideration was limited to 

 that particular tooth, one could have little hesitation in naming the new 

 species Cladodus anguineus. Possibly the bases of the teeth of C. mira- 

 hilis might not accord so well. Pta-nodus springeri and P. arviatus (Pris- 

 ticladodus springeri and var. armatus St. J, & W.) present forms of bases 

 which are intermediate between those of Chlamydoselachus and Cladodus, 

 as shown in the numerous species figured by St, John and Worthen. 



TJie Scales. 



Plate VI. Figs. 9-13. 



Over the entire body the scales are small and irregular in size and 

 shape. On the flank and belly they are polygonal plates, or depressed 

 lumps (figs. 9, 10), surmounted by one, two, or three sharp promi- 

 nences, the median of which is the stronger, in places becoming a keel. 

 On the tail this keel is produced beyond the base as a spine (figs, 10, 

 11), This spine is very sharp, has three longitudinal ridges, and 

 is excavated slightly or flattened beneath. About the mouth and in 

 particular around its angles the spines are larger, more conical, and more 

 erect, — more like teeth (fig. 12), Each of a few of these scales has a 

 small cusp on one side near its base. In the mouth, just behind the last 

 row of teeth, there are spines which are more slender, and which have 



