54 MAZATLAN BIVALVES 
Genus ? CLEMENTIA, Gray. 
B. M. Cat. Ven. p. 197. 
82. P CLEMENTIA GRACILLIMA, 7%. S. 
Ly Oy & subtrigond, tenuissimd, alba, diaphand, concentrice 
liratd, liris rotundis, approximatis ; postice pr olongatad. Intus 
dent. 3-4 divergentibus, minutis : ligamento vix monstrante. 
This shell comes nearer to Clementia than to any other 
genus I know; nor is there any reason why it should not be 
found on the American shores of the Pacific. Some may rank 
it with Tellina.. The teeth are more equally divergent than in 
the typical species. Long. 09, lat. 13, alt. °5 
Hab.—Mazatlan ; from backs of Chame and Spondylus La- 
marckii; extremely rare; L’pool Col. 
Tablet 216 contains 1 perfect and 2 broken valves. 
Genus TRIGONA, Megerle. 
Trigona, Megerle. teste Desh. B. M. Cat. Ven. p. 45— Mih- 
feldt, teste Woodw. Man. Moll. pt. 2, p. 305. 
=Trigonella, Conr. Hinds. 
= Cytherea (pars) Lam. 
Known from Cytherea and Dione by the trigonal shape ; 
numerous irregular cardinal and long lateral teeth; and by 
the velvety periostraca outside the epidermis, of a dull white 
colour, which, being mistaken for dirt, is generally very care- 
fully cleaned off by collectors. Under the microscope, this 
appears like an irregular mass of needle-like crystals. 
83. TRIGONA RADIATA, Sow. 
Cytherea radiata, Proc. Zool. Soc. 1835, p. 23.—Hanl. Deser. 
Cat. p. 106.—Sow. Thes. Conch. p. 619, pl. 128, f. 23—31.— 
C. B. Ad. Pan. Shells, p. 273, no. 446. 
Trigona radiata, Desh. B. M. Cat. Ven. p. 51, no. 19. 
Venus Solangensis, B. M. Cat D’ Orb. Wil. p. 68, no. 607. 
Trigona Byronensis, Gray, Anal. t. 8. p. 304, 1838. 
=Cytherea corbicula, Menke (non. Lam.) in Zeit. f. Mal. 1847, 
p. 189, p.54: also Sow. Thes. Conch. p. 614, no. 7 (pars). 
pl. 128, f. 39 (f. 37, 38 excl.) 
