206 



In a series of vertebras similar to those of this genus, those included in 

 the basis of the caudal fin are not more than three in number. 

 The species are distinguished as follows : 



Premaxillary teeth 5, second most prominent ; maxillary 

 not concave ; dentary with 30 teeth, and biconvex 

 alveolar border, with obtuse extremity I. anaides. 



Premaxillaries 1 ; maxillary straight, large, with 40 teeth ; 



dentary straight, not produced at end ; teeth 26 /. ctenodon. 



Premaxillaries 5, first most prominent; maxillary concave, 

 narrow ; teeth small ; dentary with a hook at apex, 

 teeth 25 /. hamatus. 



Premaxillaries 7, first most prominent, compressed ; smaller. I. prognathus. 



Premaxillaries 12, second most prominent; the bone much 



narrowed above, smaller /. multidentatus. 



The English species of this genus is figured by Dixon in the Geology 

 of Sussex, PI. xxxii, Figs. 9 and 9*. I can find no letter-press nor name 

 relating to it, and cannot determine its specific characters from the fragment- 

 ary character of the piece of mandible figured. 



ICHTHYOBECTES AJTAIDES, Cope. 



Indicated by two individuals : one with both dentary bones and teeth, 

 with vertebrae; the other with many portions of cranium, fin -rays, vertebrae, 

 and other elements more or less separated. The latter were all taken from 

 the upper face of a spur of a limestone-bluff, elevated about five feet from 

 the ground-level, where they were denuded and exposed as on a table. 



It is the largest species of the genus, and the anterior premaxillary teeth 

 are larger than-the posterior. The premaxttlarxj bones are oblicpie ovoids, very 

 convex on the external face, thinning laterally and above. The superior mar- 

 gin presents a thickening bearing an articular surface, while behind it is 

 an open gutter-like inflection. The large teeth are quite cylindrical. Both 

 these bones are preserved. But part of the right maxillary remains. It is 

 thickened above in front of the condyle, and is regularly convex at that point. 

 The teeth are small, there being 10.5 in an inch. The margin is not 

 concave. 



The mandibular rami are preserved almost entire. They are short and 

 deep, and have a short angular process, which is relatively shorter than in 



