215 



excavato ; sinu pallii haud parvo, rotundato ; maryine tenue 

 crenato. 



Long. -62, lat. 74, alt. -4. 



Hab. Sta. Barbara, iegit T. Nuttall; sp, unic. Museo suo. 



Mysia tumida, Conr., Nutt. MS. 



This shell has the general shape and aspect of a Tapęs, -mth a 

 sculpture resembling Venus {Chione) (jnidia and its congeners, and 

 a hinge not exactly corresponding with any of the defined genera. 

 The anterior teeth are short and divergent ; the centrai teeth are 

 bifid and interlock ; the posterior tooth is bifid iu one valve, single 

 m the other, with an obscure lateral tooth inside the almost concealed 

 ligament. The pallial sinus is not so large as in Tapea. 



" 32. Tapęs straminea, Conr. 



Venus straminea, Conr. Journ. p. 250. pi. 19. f. 14 (non 15). 



Tapęs straminea, Sow. Thes. Conch. p. 699. pi. 151. f. 151. 



Chione straminea, Desh. B. M. Cat. Ven. p. 141. no. 66. 



= Venus dispar, Gould, MS. 



Hab. Sta. Barbara et San Diego. Long. I -5 poli. Mus. Brit. 

 Nuttall, Cuming, &c. 



This belongs to a group of closely allied species intermediate be- 

 tween Venus and Tapęs, and is replaced in the Mexican fauna by 

 Tapęs histrionica (B.M. Mazatlan Cat. p. 7Q. no. 109). 



Genus Saxidomus, Conr. 

 Saxidomus, Conr. Journ. p. 249 ; Desh. B.M. Cat. Ven. p. 186. 

 " Testą cequivalvis, postice hians ; cardine, valva dextra dentihus 

 compressis iv.-v., valva sinistra iv. y cicatricibus muscularibus 

 ii. magnis, rotundatis ; sinu pallii profundo. 

 "Differs from Tapęs in its gaping extremity and rounded pallial 

 sinus." This description is enlarged by Deshayes so as to include 

 eight species. 



33. Saxidomtjs Nuttalli, Conr. Journ. p. 249. pi. 19 f 12- 

 Desh. B.M. Cat. Ven. p. 188. no. 4. 



This species inhabits the Californian coast as far as San Diego ; 

 where it is found burrowing into soft clay-stone, along with Pholades, 

 Cuminįfice, &c. The differences between this and the sub-boreal 

 species, iS. giganteus (Desh. B.M. Cat. Ven. p. 187. no. 2 ; quoted 

 by Middendorff from Sitka and Kamtschatka), appear extremely 

 shght. They are uuited by Jay. 



Genus Trigona, Megerle. 



Trigona, Megerle, Desh. B.M. Cat. Ven. p. 45. 

 = Trigonella, Conr. : indicated in Journ. 1837, p. 253 ; described 

 in Journ. 1849, p. 213. 



