PATELLA. k 20l 



Boutan speaks of an intermediate layer between ilie 

 middle and internal, but", unless this corresponds with 

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

 have not found, it. 



II. Soft Parts of Exterior. — Before removal of the 

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

 continuous mantle-skirt can be made out in ventral 

 (fig. 3) and side view of the body. 



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

 edge which separates a smooth ventral surface from the 

 smooth sides. Laterally and posteriorly the latter rise 

 almost vertically to the insertion of the mantle, and 

 anteriorly become continuous with the head. 



(b) 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 oil, 

 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. Tfie upwardly 

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

 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 J^uchal cavity. 



The transversely oval mouth situated at the front end 

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

 a reniform outline resulting from an indentation of its 

 ventral half. The lip 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 



