534 FISHES. 



as a normal ovarian gestation, the sac containing the young 

 not being the oviduct but the ovarian sheath, which fulfils 

 the functions of the ovary. This organ presents two modes 

 of arrangement : in one there is a series of triangular mem- 

 branous flaps communicating with each other, between which 

 the young are arranged, mostly longitiMinally, the head of 

 one to the tail of another, but sometimes with the bodies 

 curved, to the number of eighteen or twenty ; in the other, 

 the cavity is divided by three membranes converging to a 

 point, into four compartments, not communicating with each 

 other except towards the genital opening, the young being 

 arranged in the same longitudinal manner. The propor- 

 tionate size of the young is very remarkable. In a female 

 specimen 10| inches long, and 4i inches high, the young 

 were nearly 3 inches long and 1 inch high. Seventeen 

 species are known, the majority of which belong to Ditrcma, 

 and one to Hysterocaiyus. They do not attain to a large size, 

 varying from three-quarters to three pounds in weight. 



Fourth Family-^Chromides. 



Body elevated, oUong or elongate, scaly, tlie scales being 

 generally ctenoid. Lateral line interrupted or nearly so. One 

 elorsal fin, with a s^nnoiis portion ; three or more anal spines ; 

 the soft anal similar to the soft dorsal. Ventral fins thoracic, 

 loith one spine and five rays. Teeth in the jaivs small, palate 

 smooth. Pseudoliranehiev none. Stomach coecal ; pyloric ap- 

 pendages none. 



Freshwater-fishes of rather small size from the tropical 

 parts of Africa and America ; one genus Itoui Western India. 

 The species with lobate teeth, and with many circumvolu- 

 tions of the intestines, are herbivorous, the other carnivorous. 



Etroplus. — Body compressed, elevated, covered with ctenoid 

 scales of moderate size. Lateral line indistinct. Dorsal and anal 



