332 OSTREAD^. 



" The liver is always of the shades of green, and 

 situated at the centre of the dorsal range; the passage 

 from the mouth to the stomach, which is under, and 

 partly enveloped by it, is very short ; from it the anal 

 tube descends to the centre of the body, where it makes 

 a short turn, and ascends by the body, through the 

 ovarium to the dorsal range, and again descends, slightly 

 attached to the membrane of the latter organ, and de- 

 bouches at some distance from the base of the posterior 

 ventral range. 



" Finally, as regards the animal, it is necessary to 

 observe, that in this singular and unsymmetrical genus, 

 even its organs, like its shell, display varieties of form ; 

 from the entire animal being deposited in the convex 

 valve, it only rests on the flat one, consequently, the 

 organs vary, in some measure, with the fig-ure, form, and 

 depth of the concavity of the upper valve." 



This Protean species is distributed throughout the Eu- 

 ropean Seas, and on our own coast it is common everywhere. 

 It occasionally occurs free with the perforation soldered 

 up, as we have dredged it in the Bristol Channel. It 

 ranges from low-water-mark to as deep as twenty or 

 thirty fathoms (M 'Andrew). Mr. Jeffreys has taken the 

 variety cylindrica in one hundred fathoms off the Zetlands. 



A. ACULEATA, Muller. 



Small ; surface radiated with regular raised strire, which are 

 usually armed with prickles : no triangular cavity on the under 

 valve beneath the hinge. 



Plate LV. f5g. 4. 



Anoiuia aculeaia, Muller, Zool. Dan. Prodrom. p. 249. — Mont. Test. Brit. p. 

 157, pi. 4, f. 5. — Maton and Rack. Trans. Linn. Soc. vol. 

 viii. p. 103. — TuRT. Conch. Diction, p. 4 ; Dithyra Brit. p. 



I 



