58 MAZATLAN BIVALVES 



85. TKIGONA ARGENTINA, Sow. 



Cytherea argentina, Proc. Zool. Sac. 1835, p. 46. Hani. Descr. 



Cat. p. 105: Wood's Suppl. pi. 15, f. 15. Phil. AbUld. 



Condi. Cyth. pi. 3, f. 5. Sow. TJies. Conch, p. 622, pi 129, 



f. 62. ?Menke Zeitsch.f. Mai. 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,itvith 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 scar is less deeply impressed and more evenly bounded. 

 Long. 2-12, led. 2'6, alt. T52. 

 Hal). Grulf of Nicoyia, in sand banks at low water, Cuming. 



PGuaymas, Lieut. G-reen, (Gould ms.*). Mazatlan ; Mel- 



chers. Do. very rare ; L'pool fy Havre Coll. 



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. TKIGONA ?? CEASSATELLOIDES, Conr. 



Ann. Nat. Hist. Soc. Philad. t. 7, p. 253, pi. 19, f. 17. Hinds, 

 Voy. Sulph. Moll. p. 65, pi. 21, f. I Desh. B. M: Cat. Ven. 

 p. 46, no. 1. 



Cytherea crassatelloides, Hani. Descr. Cat. p. 106: Wood 



Suppl. pi. 15, f. 32. Sow. Thes. Conch, p. 612, pi. 127, f. 13. 



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 5 inches. (Woodw. Nutt.) 



* Dr. Gould writes "Venus straminea, Conr. = argentina ?" Tapes straminea, 

 Conr. is the Californian representative of T. histrionica or T. grata. It is pJO- 

 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 

 that the first shell is meant : also that Menke's Cytherea argentiua is one form 

 of T. radiata. 



