190 



The view of tlie superior walls of the cranium given by Professor Agassiz 

 presents characters quite distinct from what I have observed in PortJieus. 



A species oi Ichthyodectes, from the chalk of Sussex, England, is figured, 

 but not described, by Dixon in the Geology of Sussex. 



A number of forms, erroneously placed by Agassiz and Dixon in the 

 genus Saurocephalus, have been referred by Leidy to a genus he calls Proto- 

 sphyrmia,^ with two species, P. ferox and P. striata. The latter much 

 resembles a Saurocep/nilus, having equal teeth; while the former prol)ably 

 includes several species, and probaldy genera. The teeth first referred to it 

 resemble those of P. striata; while others resemble those of Portheus. An 

 examination of the figures of the mandibles of some of these in Dixon's work, 

 shows that the large antl small teeth occupy ditTercnt areas, separated by 

 grooves, in a manner quite distinct from anything seen in Portheus; but it 

 can scarcely be regarded as typical o[' Protos2)hyr(sna, which name, moreover, 

 has never been accompanied by the necessary description. - 



Dr. Leidy applied the name Xiphactinus to a genus indicated by a spine 

 in some degree like those regarded above as ventrals of Saiirodontidfe. 

 Whether it belongs to any of the genera above enumerated, or, if so, to which 

 of them, is a question which can only be settled by future investigation. 



The history of the definition of this family may be found in the follow- 

 ing references: Proceedings of the American Philosophical Society, 1870, p. 

 529; Hayden's Survey of Wyoming, etc., 1871, p. 414; Proceedings of the 

 American Philosophical Society, February, 1872. 



PORTHEUS, Cope. 



Proceedings oi' the Aincricaii Philosophical Society, 1871. p. 173; 1. c, 1872, Febriiarv. 



Teeth sulicylindric, without serrate or cutting edges, occupying the pre- 

 maxillary, maxillary, and dentary bones. Sizes irregular; the premaxillary, 

 median maxillary, and anterior dentary teeth much enlarged. No foramina 

 on inner face of jaws. Teeth on the premaxillary reduced in number. Oper- 

 cular and preopercular bones very thin. Cranial bones not sculptured. 



The fishes of this genus were rapacious, and, so far as known, of large 

 size. They constitute the most formidal)le type of physostomous fishes 

 known. Five species are known to the writer from the Niobrara Cretaceous 

 of Kansas. These are represented by numerous fragments of many individ- 



' Trausactioiis of the American Philosophical Society, 1856. 



