58 MAZATLAN BIVALVES 
85. TRIGONA ARGENTINA, Sow, 
Cytherea argentina, Proc. Zool. Soc. 1835, p. 46.—Hanl. Descr. 
Cat. p. 105:— Wood's Suppl. pl. 15, f. 15.— Phil. Abbild. 
Conch. Cyth. pl. 3, f.5.—Sow. Thes. Conch. p. 622, pl. 129, 
f. 62.—? Menke Zeitsch. f. Mal. 1847, p. 189, no. 55. 
Trigona argentina, Desh. B. M. Cat. Ven. p. 50. no. 16. 
This shell may be known at once from those varieties of 
T. radiata which most approach it by the very remarkable and 
constant shape ; being most regularly excurved along the ven- 
tral margin, incurved on the anterior and straight on the pos- 
terior dorsal lines. Colour dull white, with light olive green 
epidermis ; often with two rays of violet within. The anterior 
cardinal tooth is much larger than in T. radiata, and the pos- 
terior tooth does not display rugose sulcations. The anterior 
adductor sear is less deeply impressed and more evenly bounded. 
Long. 2°12, lat. 2°6, alt. 1°52. 
Hab.—Gulf of Nicoyia, in sand banks at low water, Cuming.— 
?Guaymas, Lieut. Green, (Gould ms.*).—Mazatlan; Mel- 
chers.—Do. very rare; L’pool & Havre Coil. 
Tablet 245 contains 3 minute valves, the smallest ‘04 across, 
which may belong to this species. 
Tablet 246 contains 2 specimens. The smallest displays the 
violet rays, and an abnormal lamina within. 
86. TRIGONA P? CRASSATELLOIDES, Conr. 
Ann. Nat. Hist. Soe. Philad. t. 7, p. 253, pl. 19, f. 17.— Hinds, 
Voy. Sulph. Moll. p. 65, pl. 21, f. 1.— Desh. B. M. Cat. Ven. 
p. 46, no. 1. 
Cytherea crassatelloides, Hanl. Deser. Cat. p. 106 :— Wood 
Suppl. pl. 15, f. 32.—Sow. Thes. Conch. p. 612, pl. 127, f. 1—3. 
Tablet 247 contains 2 small valves, (the smallest *04 across) 
which have the shape aud thickness of this species. Their 
identity however is doubtful, T. crassatelloides belonging 
strictly to the Californian fauna, where it attains a diameter 
of 5inches. (Woodw. Nutt.) 
* Dr. Gould writes ‘‘ Venus straminea, Conr. = argentina P” Tapes straminea, 
Conr. is the Californian representative of T. histrionica or T. grata. Itis pro- 
bable therefore that our shell is meant, as Tr. argentina is a well known and 
constant form. It is possible however that it may not be known to Gould, and 
uel the oe shell is meant: also that Menke’s Cytherea argentina is one form 
of T, radiata, 
