TRIBE MYTILACEA. 239 



not cross each other : white, thin, fragile and scarcely pearly un- 

 der a greenish brown epidermis. Peru and Chili in stones. Closely 

 allied to the last. 



M. Laevigata, (not of Gray) Lithodomus L. Quoy. Ast. t. 78./. 

 17, 8. Elongated subcylindrical straight, thin, smooth with a 

 greenish brown epidermis ; a lateral oblique furrow ; within brown- 

 ish white, pearly with a violet stain at the uncinated anterior extremi- 

 ty. — In Madrepores. — New Guinea. 



M. Fusca. Desk, in Lam. vol. 7. p. 28. — Mytilus. F. IV. t. 12. 

 /. 12. — Gmel. 3359. — D. p. 306 — Modiola Cinnamonea. Far. 

 Lam. 18. — List. t. 359. f 197. Small subcylindrical, much curved 

 and finely striated; obtuse andheart shaped at the posterior extremity, 

 rounded at the other ; the beaks recurved and slightly prominent ; 

 white and thickish under a rich brown cuticle, f — Indian Ocean in 

 Madrepores, Very like Cinnamonea. 



M. Truncata. — Lithodomus. T. Gray in App. to Dieffenbach. 

 Zeal. Oblong, subcylindrical, thin ; short and roundly truncated 

 posteriorly, contracted in the middle, and tapering anteriorly; cuticle 

 dark brown ; umbones rather prominent, inflexed ; within purplish, 

 nacreous. New Zealand. Easily recognized by its truncated ex- 

 tremity, and prominent umbones. The front portion is usually covered 

 with regular green lamince which are perhaps Algce. 



M. Opifex. Say. Jour. A. N. S. Philad. 2. p. 369. t. 19. f. 2. 

 Oval, reddish brown, ventral edge slightly contracted behind the 

 middle, from which spot to the beaks the surface is blackish and 

 transversely wrinkled ; sides longitudinally striated, except the an- 

 terior cordate hinge margin, which is flattened and covered with a 

 stratum of compact sand : anterior tip equally arcuated above and 

 below : irridescent within. 0, 23 . . 0, 47. — Minorca. 



M. Canalifera. — Lithodomus C. Nobis Zool P. 1 844. Sub- 

 cylindrical, rather elongated, subarcuated, covered with a smooth 

 rufous or reddish yellow epidermis, which is concealed by a calca- 

 reous coating, which on the umbonal slope assumes the appearance 

 of four slightly elevated radiating walls roofed by another layer of 

 calcareous matter, and terminating in three narrow channel-like 

 apertures at the anterior extremity : posterior end rounded, anterior 

 extremity attenuated and obtuse : dorsal and ventral edges sub- 

 parallel, the former incurved, the latter slightly convex : anterior 

 surface divided by an oblique furrow from the more elevated pos- 

 terior. | . . 1 ^. — S. America. 



M. Plumula. — Lithodomus P. Nobis Zool. P. 1844. Extremely 

 like the last, but the anterior extremity less obtuse, and the calca- 

 reous cellular coating of the umbonal ridge, resembling a ruffled 

 feather in its arrangement, being composed of elevated thin ridges 

 which slope anteriorly and diverge from their point of junction, 



