T,ELLINA. 373 



and Sars have made similar observations with regard to 

 the Crustacea and other Invertebrata which are com- 

 mon to northern and southern latitudes. An explana- 

 tion (although perhaps an imperfect and unsatisfactory 

 one) of this law has been offered in the ' Introduction ' 

 to my first volume, p. xxxii. 



The synonyms of this pretty species are few and ob- 

 solete. I am aware of two only, viz. T. orbiculata, Re- 

 nier, and T. serratula, Chiereghini. 



2. T. CRASSA *,( Gmelin.) H ' ^ 



Venus crassa, Linn. Syst. Nat. (ed. Ghnel.) p. 3288. T. crassa, F. & H. i. 

 p. 288, pi. xx. f. 1,2. 



BODY yellowish -white : mantle thick ; edges closely fimbri- 

 ated : tubes funnel-shaped and long ; orifice of each narrow, 

 and fringed with 6 short tentacular cirri; the excretal or 

 upper tube in an individual examined by me was three or four 

 times the length of the other tube ; mouth of the alimentary 

 tube much contracted and like a snout in shape : gills nearly 

 circular, of a very thin texture ; lower pair twice the size of 

 the upper ; both are coarsely but not distinctly pectinated : 

 palps narrow, slender, pointed, of an elongated triangular form, 

 quite smooth externally, but conspicuously striated on the inner 

 side : liver dark brownish-green : foot very large. 



SHELL obtusely triangular rather than oval, compressed, 

 thick, opaque, moderately glossy ; the left valve is somewhat 

 larger and deeper than the other : sculpture, numerous strong, 

 threadlike, concentric ribs, which are more crowded and become 

 laminar at the sides also in the young ; the narrow interstices 

 of these ribs are impressed with finer parallel striae, and crossed 

 by deeper, more regular, and close-set longitudinal striaB, none 

 of which, however, are visible except by the aid of a magni- 

 fier : colour the same as in the last species : epidermis fibrous, 

 yellowish-brown, slight, and effaced in nearly every part by 

 continual friction : margins curved in front, and obtusely an- 

 gular with rounded points at each end ; posterior side decidedly 

 flexuous, especially in the right valve : beaks small, incurved, 



* Solid. 



