422 



SPINY-FINNED GROUP. 



ductive arrangements, viviparous wrasses. Agreeing with the wrasses in the 

 presence of false gills and the cycloid scales, they differ in having four gills, and 

 the anal fin furnished with three spines and numerous soft rays. In form, the 

 compressed body is either elevated or oblong, and the lateral line continuous. The 

 single dorsal fin has a spinous portion in front, and a scaly sheath along the base, 

 separated by a groove from the body-scales. Small teeth are present in the jaws, 

 but the palate is toothless. Generally not exceeding a pound in weight, these 

 fishes are confined to the temperate region of the North Pacific, where they are 

 much more numerous on the American than on the Asiatic side. While the 

 majority belong to the genus Ditrema, of which an example (D. argenteum) from 

 San Francisco is represented in the illustration, one species constitutes the genus 

 Heterocarpws, distinguished by the number of dorsal spines being from sixteen to 

 eighteen, instead of only from seven to eleven. All these fish produce living 

 young, which are contained in the sheath of the ovaries, instead of in the oviduct. 



TRISTRAM S CHROMID. 



Chromids. 



Although some members of the preceding family may occasionally 

 enter rivers, the chromids, family Chromididce, differ from all the other 

 fish with united lower pharyngeals in being exclusively fresh-water forms. Their 

 distribution is somewhat peculiar, and very similar to that of the lung-fishes 

 (exclusive of the Australian form). Thus they are found in the rivers of Tropical 

 America and Africa, together with Madagascar, Syria, and Palestine, one outlying 

 genus occurring in India ; and it may be remarked that all the genera from the 

 New World are distinct from those of the Old World. Mostly of comparatively 

 small size, although one species of the type genus from the Nile grows to a length 

 of about twenty inches, the chromids may be distinguished from all the other three 

 families of the present group by the absence of false gills. The body, which is 

 somewhat variable in form, is generally covered with ctenoid scales, although in 

 some cases these may be cycloid ; and the lateral line is more or less interrupted. 



