330 



FISHES. 



liodns, Polyrhizodns, etc. ; in the Trias and Chalk by StrojyJi- 

 odus, Acrodus, Thcdodus, and Ptycho- 

 dus. Of the 25 genera known, 22 have 

 lived in the periods preceding the 

 Oolitic. 



Cestracion (Heterodontus). — Each 

 dorsal fin armed with a spine in front ; the 

 second in advance of the anal. Mouth 

 rather narrow. Spiracles small, below the posterior part of the 

 eye. Gill-openings rather narrow. Dentition similar in both 

 jaws, viz. small obtuse teeth in front, which in young individuals 



Fig 121 — Coihlinaus 

 contortus. 



Fig. 122. — Cestracion galeatus, Australia. 

 are pointed and provided with from three to five cusps. The 

 lateral teeth are large, padlike, twice as broad as long, arranged 

 in oblique series, one series being formed by much larger teeth 

 than those in the other series. 



Four species are known from Japan, Aiuboyna, Australia, 

 the Galapagoes Islands, and California ; none exceed a length 

 of 5 feet. The egg has been figured on p. 1G8 (Fig. 80). 



Eighth Family — Spixacid.^;;. 



No memhrana niditans. Two dorscdfin>i ; no anal. Mouth 

 hut sliglitly arched ; a loivj, derp, straight, oblique groove on 

 each side of the month. Sjnracles present ; gill-op>enings narrow. 

 Pectorcd fins not notehcd- at their origin. 



The oldest representative of this family {Palwospinax) 



