ACTINOPTERI. 167 



mental bone. Lower jaw the longer. Premaxillaries, vomer and 

 palatines with broad bands of strong- cardiform teeth which are 

 more or less movable. Lower jaw of strong teeth of different 

 sizes. Tongue with a broad band of small teeth. No barbels. 

 Gill-openings very wide. Gill-membranes separate, free from 

 isthmus. Gill-rakers tubercle-like. Pseudobranchiae glandular, 

 hidden. Branchiostegals 12 to 20. Stomach not ccecal, without 

 pyloric appendages. Air-vessel simple. Basis cranii simple. 

 Head naked above. Cheeks and opercles more or less scaly. 

 Scales small. Lateral line weak, obsolete in young and developed 

 in adult. Dorsal posterior, opposite and similar to anal. No 

 adipose fin. Caudal fin emarginate. Pectoral fins small, inserted 

 low. Ventrals rather posterior. 



A single genus, Bsox, represented by 5 or 6 living species and 

 4 extinct. I have, however, included Ischyrhiza as only provi- 

 sionally, following Hay's suggestion. 



Genus ISCHYRHIZA Leidy. 



Ischyrhiza Leidy, Proc. Acad. Nat. Sci. Phila., 1856, p. 221. Type Ischyrhiza 

 mira Leidy, monotype. 



Tooth with crown apparently laterally compressed, conical, 

 covered with smooth shining enamel. Fang more robust than 

 crown, curved pyramidal, quadrate in section, with base rugged 

 and divided antero-posteriorly. Pulp cavity expanded within 

 fang, closed below and narrowing towards crown. 



An imperfectly defined genus, known only from detached teeth, 

 though subsequently vertebrae have also been identified as iden- 

 tical. The three species described are extinct. 



Ischyrhiza mira Lediy. 



Ischyrhiza mira Leidy, Proc. Acad. Nat. Sci. Phila., 1856, p. 221. Cretaceous 

 Greensand of Burlington Co., N. J. (L. T. Germain.) 



Leidy, Holmes's Post-pliocene Foss. S. C., i860, p. 120, PI. 25, figs. 3-9. 

 (Greensand of New Jersey.) 



Cope, Proc. Amer. Philos. Soc. Phila., XII, 1872, p. 355 (name only). 



Cope, Rep. U. S. Geol. Surv. Terr., II, 1875, p. 280. (Greensand, No. 5, 

 New Jersey, near Harrisonville.) 



