PECTUNCULUS. 249 



plain, of a yellowish grey colour, thickly dotted with 

 minute dark purple specks, but plain yellowish internally. 

 Mr. Clark has observed that at " the posterior side for 

 half its length at the very verge of the mantle, are about 

 twenty five most minute equidistant black points, besides 

 two short brown transverse bars." The margins of the 

 mantle are produced into slightly expanded lips in the 

 branchial and anal regions, and then tinged internally with 

 purple, but they do not form siphons ; though we have 

 seen them assume the appearance of sessile orifices, owing 

 to the habit the animal has of approximating their edges. 

 " Under and between the termination of the posterior ends 

 of the branchiae is a very short cylindrical anal process, 

 with a minute round reflexed margin" (Clark). The foot 

 varies in colour from pure white to orange yellow ; it is 

 semilunar in shape, thick and deeply grooved ; the margins 

 of the groove are furbelowed ; the posterior extremity of 

 the foot is often dotted with purplish brown. The branchiae 

 vary in colour from white to brownish yellow ; their fila- 

 ments are free ; each leaflet of each pair is equal, and of a 

 suboval form. " From their anterior termination a pair 

 of light brown, long linear palps, smooth on both sides, 

 originate and pursue their course around the mouth and 

 meet the fellow pair on the other side." 



This fine shell is so very generally distributed around our 

 coasts, that to enumerate localities would be superfluous. It 

 is absent from none of the districts, though more abundant 

 in some places than in others. It is generally gregarious, 

 preferring a nullipore bottom in from fifteen to twenty-five 

 fathoms, but ranging from eight to as deep as sixty fathoms. 

 It is generally distributed through the European seas, and 

 as a fossil occurs frequently in the mammaliferous crag and 

 northern drift. 



