14. HETERODONTID^ GYROPLEURODUS. 33 



"In the latter genus, the branches of the lower y.iw ;irc at tirst con- 

 tignoas and diverge from each other at an acute angh', wliik; in front of 

 the obUque whorls of molars, and between the acute teeth of th(5 front 

 which encroach on the sides, a cordiform area exists. The lateral or 

 molar teeth are numerous, and arranged in oblique whorls, which rapidly 

 increase in size to the fifth, behind which they again decrease. The 

 branchial apertures are also comi)aratively large, the lirst being longer 

 than the length of the branchial region. 



"In Gyroplenrodns^ the branches of the lower Jaw are widely separated 

 by an interval rounded in front and becoming wider behind, the sides 

 themselves being curved outwards; the acute teeth are confined to 

 the front and the molar teeth are few and disposed in about four whorls, 

 tlie first three of which slightly increase, while the fourth is almost 

 rudimentary. The branchial area is almost oblong." 



Head short and high, broad, but with subvertical sides; the forehead 

 \ery declivous from eyes, and with the snout wide and transverse, but 

 prominent; two blunt, diverging ridges are continued from each side of 

 the snout and abruptly merge into the more conspi(;uous superciliary 

 ridges, the interval between which is lu'arly plane; teeth in front digi- 

 tated, with three or four cusps, quiucuncially distributed in rows slightly 

 converging toward the middle; in the upper jaw, on the sides, molars 

 ol)l(»ng ;nid tlattened, arranged in about four oblique whorls, uniform or 

 increasing backward, except the last, which is smallest; on the sides of 

 the lower jaw, also, arc^ molars ol)long, Avith flattened crowns, and arranged 

 in transversely oblique whorls, but decreasing backward {Gill). One 

 s[)ecies known. (^0/yor, ring or whorl; iz^eupd'^, side; ooofjc, tooth.) 



41. a, Irsmcisci ((inl.) Gill. 



Dorsal tins considerably produced backward at their jjosterior angle; 

 the compressed spine forming about half of the base of each fin; anal 

 tin large, directed very ol)li(|uely backwards, I'caching the root of caudal ; 

 <'au<lal tin forming about one fourth of the length; color brownish, varie- 

 gated with s])arsely s(;attered small black spots all over the body and 

 (ins. ('oast of ('alifornia {Gill). 



(CcstracioH ./VaHCJvcf (iiravd, Proc;. Ac. Nat. Sci. Phila. 1854, 196; Ccstracionfrancitico 

 Giintlicr, viii, 41(); Gill, Proc. Ac. Nat. Sci. Phila. 1802, 492.) 



Bull. Nat. Mus. No. 10 3 



