256 



CLASSIFICATION OF VERTEBRATES. 



CLUPEID^E (herrings), head naked ; lateral line lacking; no adipose dor- 

 sal ; weak teeth or none. The species number about 125, but are very 

 numerous as individuals. Clupea (dates from the cretaceous), shad, ale- 

 wife, and herring, Brevoortia, the menhaden. Allied are Albulia, Dorosoma, 



FiG. 257. Herring, Clupea harengus. 



and Engraulis. Arapaima from South America reaches a length of 15 

 feet. The ancestral Leptolepis from the Jurassic shows marked ganoid 

 features. ALEPOCEPHALID^E, deep-sea forms. SAUROCEPHALID^E, extinct; 

 Xiphactinus (Portheus) from American cretaceous. 



The SALMONID.E, containing the salmon, trout, etc., are among the 

 most valuable of food fishes. They have an adipose fin ; teeth variable ; 

 lateral line present ; no oviducts, the eggs passing out by the pori ab- 

 dominales. Coregonus, the white fishes ; Salmo, the salmon and trout (the 

 Pacific salmon sometimes placed in sub-genus Oncorhynchus). Closely 



FIG. 258. Atlantic salmon, Salmo salar, after Goode. 



allied is the smelt, Osmerns. The fossils not readily distinguished from 

 the Clupeidas. 



A number of forms, mostly from the deep sea, are grouped as IXIOMI, 

 many of which are furnished with phosphorescent organs. In Ipnops the 

 eyes are absent, but the head is covered with a luminous plate. Scopehis 

 Chauliodits. Scopelid-like forms occur in the cretaceous. 



SUB-ORDER 2. APODES. 



Degenerate eel-like physostomi without ventral fins, mouth and oper- 

 culum reduced, scales minute or lacking; scapular arch free from the skull. 

 The true eels ( ANGUILLID/E) have the gill openings well developed ; pectoral 



