118 PISCES. 



of a median series of dorsal scutes between the occiput and the 

 dorsal fin, is Diplomystus, occurring in the Upper Cretaceous of 

 Mount Lebanon and Brazil, the Green River Shales (Eocene) of 

 Wyoming, the Upper Eocene (or Oligocene) of the Isle of 

 Wight, and apparently still surviving in the freshwaters of 

 Chili and New South Wales. Scombroclupea, from the Upper 

 Cretaceous of Mount Lebanon and Comen, in Istria, differs from 

 Clupea in possessing a series of detached finlets behind the 

 anal fin. 



An extinct family, closely related to the Chirocentridae is 

 that of the Saurodontidae or Ichthyodectidae, characteristic 

 of the Cretaceous period, with some gigantic representatives in 

 the Chalk both of Europe and America. These are predaceous 

 fishes with teeth fixed in sockets on the border of the premax- 

 illa, maxilla, and dentary, while the inner bones of the mouth 

 are toothless. The supraoccipital, which completely separates 

 the parietals, has a large median longitudinal crest. A small 

 symplectic is present. The vertebral centra in the abdominal 

 region do not exhibit any conspicuous processes for the support 

 of the ribs. The opercular apparatus is complete and there are 

 branchiostegal rays, but there appears to be no gular plate. A 

 precoracoid arch has been observed in the shoulder-girdle. The 

 fin-rays are remarkably stout, only divided and articulated quite 

 at their distal end, sometimes perhaps never divided. The 

 pelvic fins are abdominal ; the caudal fin is forked. Portheus 

 and Ichthyodectes are the best-known genera, the former with 

 compressed teeth in a very irregular series, the latter with less 

 compressed teeth in a nearly regular series. Both occur in 

 the Cretaceous of Europe and America, and some species of 

 Portheus, e.g. P. molossus, attain a very large size, perhaps not 

 less than two metres in length. This genus is also represented 

 in the Cretaceous of Queensland. 



Another imperfectly known Cretaceous family commonly 

 supposed to be related to the Salmonidae, appears to be re- 

 presented by Pachyrhizodus, from the Chalk both of Europe 

 and America. The large conical teeth are anchylosed with the 

 margin of the jaw, not in sockets, but with an outer flange 

 of bone. 



