9 



Uoulaii speuks of an iulonnodiaie layer bolwocii ilie 

 middle and inlenial, l)ut, iiuless Uiis cojit^sjxmds with 

 the inner and clearer portion (B, b) ispoken of above, we 

 have not found it. 



II. Soft Parts of Exterior. Before ](Muoval of the 

 shell the prominent ventral foot, ill-defined head, and 

 continuous mautle-skirt can be made out in ventral 

 (hg-. -J) and side view of the body. 



{a) The oval muscular Foot has a well-defined wavy 

 edge which sej)arates a smooth ventral surface from the 

 smooth sides. Laterally and posteriorly the latter rise 

 almost vertically to the insertion of the mantle, and 

 auteriorly become continucnis with the head. 



[!)) The Head, as seen from the side, is a prominent 

 muscular projection overhanging the front end of the 

 foot (fig. 5). In shape it may be compared to a truncated 

 demi-cone with the cut end turned forwards, rounded off, 

 and bent somewhat downwards to form a snout, the 

 circular muscle in the wall of which is very well 

 developed, and is practically a sphincter. The flat side of 

 the demi-cone faces downwards, and is marked off by a 

 distinct transverse groove from the snout. On either side 

 of the groove is a well-marked retractor muscle band con- 

 necting the head with the side of the foot. The upwardly 

 facing curved surface of the demi-cone is continued Lack- 

 wards till it passes into and becomes the floor of a cavity 

 of which the wide opening can be seen above the head. 

 This is the jJsuchal cavity. 



. The transversely oval mouth situated at the front end 

 of the head is bounded by a continuous frilled lip, having 

 a reniforni outline resulting from an indentation of its 

 ventral half. The li}) is clearly divided into a long dorso- 

 lateral portion and a short sharply incurved ventral 

 portion. There is a depression at the junction of these two 



