162 



ture at the base of the branchial siphon, supposed to serve as an inlet for 

 respiratory currents, by the branchiae being undivided, and by a few other 

 minor differences.* 



Figure. 



Pholadomya Candida. PL 43. Pig. 232. Shell, showing its cancellately 

 ribbed structure. 



Family 11. SOLENACEA. 



Shell ; oblong-ovate or very narrowly elo7igated, with the anterior 

 portion in such cases mostly very considerably lengthened, while 

 the posterior is short and abruptly truncated. 



In this family are associated the four genera of which the shells are re- 

 presented in Plate 44. Their general characteristic is to have, the anterior 

 portion of the creature unusually more developed than the posterior ; but 

 it is in the Solens, or Razor-shells, that this peculiarity is most conspicuous. 

 The foot issuing from an opening in the mantle, which is otherwise closed, 

 is a prominent organ for burrowing • the siphons are in some short and 

 united, in others long and only partially united. A few are inhabitants of 

 brackish water in estuaries or the mouths of rivers. The genera are — 



SOLEMYA. GlATJCONOME. SoLEN. Sc-LECURTUS. 



Genus 1. SOLEMYA, Lamarck. 



Animal; mantle open in front for the passage of a truncated pro- 

 boscis-like foot, and behind with a single siphonal orifice ; mar- 

 gins of both openings cirrhated ; foot excavated at its extremity, 

 which has fimbriated edges. 



Shell ; equivalve, very inequilateral, somewhat squarely oblong, 

 rather thin, conveocly compressed, covered with a shining, dark, 

 brittle, horny epidermis, passing conspicuously over the margin ; 



* Professor Owen's detailed memoir ' On the Anatomy of the Pholadomya Candida' of 

 which I have an uncorrected proof, was contributed by the author, and set in type, along with 

 a memoir ' On the Anatomy of Lithedaphus,' for an appendix to my ' Conchologia Syste- 

 matica;' but by some unaccountable negligence the drawings were lost while in the hands of the 

 Secretary of the Zoological Society, in whose ' Proceedings ' only a brief abstract of the memoirs 

 appeared, and they have never, 1 believe, been published. 





