GUPPY : MOLLUSCA OF GULF OF PARIA. 1 69 



extremely rare., and lives in 2 to 3 fms. water, on a 

 bottom of sandy mud. No locality is given by Reeve 

 for his shell] 



171. M. exustus Linn. Orb. Moll. Cuba, pi. xxviii., f 6, 7. 



M. citrinus Chemn. Wood, Ind. Test. i\.rca, 15. 

 M. sulcata Lam. 



172. M. domingensis Lam. Orb. Moll. Cuba, vol. ii., pi. xxviii. 



f. 8, 9. 

 M. exustus Lam. 



Crenella Brown 1827. 



173. Cr. viator Orb. Voy. x^mer. Mer., pi. Ixxxiv., f 34 — 37. 



LiTHODOMUS Cuvier 1817. 



174. L. bipenniferus, Guppy. Proc S. A. Trinidad, Dec. 1877, 



P- 154—5- 



Elongate, sub-cyiindrical, nearly straight, smooth, thin, epi- 

 dermis yellowish-brown, generally incrusted with a blackish 

 deposit, running posteriorly into white pointed calcareous 

 rostriform appendages which cross each other, in different 

 specimens with the beak of either above or below. Umbones 

 round, terminal. Ventral edge scarcely curved. Dorsal 

 edge slightly angulate. Length 35-45, height 10, thickness 

 1 1 mill. 



This shell differs from Z. caudigenis, its West African 

 analogue, in being more cylindrical; the umbones are 

 usually less prominent and more nearly terminal; the 

 dorsal edge has rarely so pronounced an angle. Burrows 

 in soft limestone and corals. 



{Sub-order Fecti/nna.) 

 Perna Bruguiere 1792, 



175. P. obliqua Lam. 



P. ephippium Sow. (not Linn.) Woodward, pi. xvii., f. 2. 

 Ostrea alata Gmelin. 



