168 - MYAD^C. 



cast on shore at Exmouth during the late gales ; it arrived 

 quite lively, wrapped in fucus, and accompanied by sea-water. 

 It proved an important acquisition. I ascertained, both 

 anatomically and practically, that there is no connection 

 between the branchial and anal siphons, affording another 

 proof that there is an end to the doctrine of separate branchial 

 currents by cilia. 



M. ELLIPTICA, nobis. 



Lutraria elliptica, Lamarck. 



, Brit. Moll. i. p. 370, pi. 12 ; (animal) pi. H. f. 2. 



Mactra lutraria, Auctorum. 



Animal compressed, subovally elongated, white. The mantle, 

 ventrally, has the margins united by a fine, white, minutely 

 crenulated line, which marks the suture, except for a space 

 of about one-third of the posterior portion of the pedal fissure, 

 which is edged by rather distant fine white filaments, and 

 affords a passage for a large thick tongue-shaped white foot, 

 without a byssal groove. The siphonal sheath is very large, 

 subcylindrically tapering, and, in a shell of 3J inches trans- 

 verse measure, is, when in full activity, 6 inches long ; from its 

 base for 2 inches it is white, and for another 2 inches marked 

 with zigzag purplish-brown blotches, which at the terminal 

 portion become distinct, dark purplish-brown dots; on the 

 surface of the sheath there are two or three circular brown 

 lines, an inch apart, and it is covered with a transparent 

 corrugated skin, which appears to be a prolongation of the 

 light horny epidermis that clothes the exterior of the entire 

 area of the valves; within the sheath are the anal and 

 branchial siphons, both furnished at their terminations with 

 numerous white cirrhi, minutely spotted with dark purplish- 

 brown or red ; the branchial cilia are the longest, delicately 

 fimbriated on the margins with alternate smaller and shorter 

 ones ; the anal are of the same colour, but shorter and more 

 numerous. The branchiae are pale brown laminae, not deep, 

 the upper ones being rather the lesser ; they are hung trans- 

 versely, with their points lying in the branchial cavity ; the 

 minute vessels of the circulation give them the appearance of 



