122 MAZATLAN B1VA1VE8 



Modiola Brasiliensis, Hani. Descr. Cat. p. 234. — Dkr. in lit, 



MytUus bicolor, Brmj. Cat. 



Modiola Guyanensis, Lam. An. s. Vert. vol. vii. p. 20, no. 4. — 



Beles. Rec. t. 13, f. 9. 

 Mytilus Guj-anensis, Desk. Enc. MetJi. vers. vol. ii. p. 565. 



no. 24. 

 = Modiola semifusca. Sow. (non Lam.) Gen. f. 6. — S,ve. Conch. 



Syst. pi. 101, f. 6.— C. B. Ad. Pan. Shells, p. 251, no. 399. 



The typical form is remarkably constant in its characters, 

 while the ?var. is very changeable. Shell extremely thin, 

 very rhombic, with the ventral and dorsal lines very straight, 

 at an angle of about 30**, a weU marked diagonal ridge, and a 

 somewhat straight posterior line, at a mean divergence of about 

 105" from the dorsal line : with concentric furrows on the 

 posterior part of the shell. This is coloured olive green ; while 

 the anterior ventral part is smooth, and of an orange colour, 

 with a narrow diagonal band of light orange, separating the 

 two areas. Inside stained dorsally with reddish pui-ple. 

 Umbos not decorticated. Long. 3"3, lat. I'o, alt. I'l. 



Hah. — Brazils, Guyana, LunTcer. — Venezuela, (Porto CabeUo 

 et Caraccas,) Bay of Guayaqtdl ; _Dr. Tarns, teste Dunker. — 

 Mazatlan ; rare ; L'pool ^' Havre Coll. — Panama, rare. 

 C. B. Adams. 



Tablet 558 contains 2 specimens, young and old. 



171 h. Modiola PBeasiliensis, var. mutabilis. 



Modiola semifusca, P. P. C, Cat. Prov. ; non Soto. ; nee 

 Lam. An. s. Vert. vol. vii, p. 22, no. 11, (teste Hani.) 



Jif. ? Brasiliensis, t. solid lore, epidermide atro-fuscd indutd, 

 apicibus ^ilerumque decortirafis ; staturd minore :' forma ma- 

 xime variante ; margine vent rail recto sen ralde incurvato ; 

 plus minusve elongatd ; angulo diagonali indistinctiore ; mar- 

 gine posteriore plus minusve excurvato. 



This shell suits exactly the description of Lam., but is 

 distinct from the shell which Mr. Hanley states to be the 

 true M. semifusca. According to Hanley, Dunker, and the 

 first impressions I received from an examination of the speci- 

 mens, this may be a rough water var. of M. Brasiliensis : there is 

 however sullicieut doubt to make it desirable that the varia- 

 tions from other recorded localities should be accurately 



