CHORD ATA — VERTEBRATA — FISHES 347 



Order c, Holostei. — Tail heterocercal or nearly homocer- 

 cal. (i) Semionotus (Fig. 148), fusiform, with rhombic scales, 

 the dorsal ones forming a crest. Triassic of North America, 

 Europe and South Africa. Those from Massachusetts, Con- 

 necticut and New Jersey were formerly called Ischypterus. 



Fig. 148. — An actinopterygian fish, Semionotus (Ischypterus) lenticularis New- 

 berty, from the fresh water Triassic shales of Boonton, New Jersey, a.f., anal 

 fin; c./., caudal fin ; </./., dorsal fin ; wo., mouth ; fi., orbit of eye; pecf., pectoral 

 fin; pel.f., pelvic (or ventral) fin. (Newberry's figure.) 



(2) The mud-fish (Amia), from the rivers of the United 

 States, and (3) the garpike (Lepidosteus), from the fresh 

 waters of the southern half of North America and Cuba, 

 are living examples; both occur fossil from the Eocene to the 

 present. 



Order d, Teleostei. — The Teleostei (Jurassic to present) 

 are merely improved ganoids. Scales overlapping, in oblique 

 rows, usually thin, elastic, generally round with a smooth margin 

 or with the posterior margin toothed. Backbone typically 

 ossified. Tail homo- or diphycercal. 



The herrings are known from the Comanchean to the 

 present ; species of Diplomystus (Cretaceous to present) are 

 beautifully preserved in the fresh water Green River shales 



