301 



symphysis. There are coarser strire mingled with the finer ones on the 

 posterior faces of the mandibular teeth. Rami slender. 



This specimen exhibits the mode of succession of the teeth, which is 

 quite peculiar and different from what I have described in the other genera. 

 The first teeth appear on the alveolar surface at a considerable distance 

 apart. The second teeth appear immediately in front of these, and by their 

 presence create the irritation whicli results in the alssorption of the root and 

 shedding of the crown of the first. The teeth of the third series appear in 

 advance of tlie second, occupying the space between them and the empty 

 space previously occupied by No. 1. These may co-exis,t for some time with 

 teeth No. 2, as the specimen indicates, but the result is as before, the shed- 

 ding of the adjacent older teeth. In the case of the anterior long tooth of 

 each side, the movement is reversed. Here the successional tooth appears 

 l)ehind the position of the functional, which is consequently shed, and in the 

 old fish this tooth occupies a position behind a concave symphyseal portion, 

 which is concave and edentulous, or only provided with the small teetii of 

 the marginal row. 



Tlie skull of this species is flat, and the frontal bones are very thin. 

 They are strengthened by a longitudinal striate rib on each side, which 

 passes from the posterior jwrt of the cranium to tlie prefrontal region. There 

 are apparently no exoccipital condyles, and the basis cranii is simple and with 

 a short keel on the basioccipital. 



A comparison of this species with a new specimen of the Enchodus 

 gladiolus, Cope {Phasganodus m.), better than that previously described 

 (see p. 235), exhibits the following specific differences. (The latter species 

 was founded on a long anterior maxillary tooth.) The teeth all differ in 

 possessing on the posterior face a sculpture of parallel grooves. The known 

 s|)ecimens are larger. In the E. calliodon, the grooves ai'e fewer and stronger, 

 and the cutting-edges of the fangs are not opposite. 



The specimens above described indicate that the genus Phasganodus, 

 Leidy, as defined in the present work, is untenable, and that the species must 

 be united with Enchodus ; the greater or less convexity of the sides of the 

 fangs offering specific characters only. The Enchodus anceps (Phasgano- 

 dus, 1. c.) differs from the two species above described in the shorter and 

 much stouter teeth. Its long fangs are not certainly known. 



