6l4 SAMPSON. ■ [Vol. XI. 



rior portion of the attachment of the antero-oblique and of the 

 latero-pedal of the posterior group is interrupted. 



Shell VIII. 



The peculiar shape of VIII and its terminal position neces- 

 sarily lead to differences in the muscular arrangement ; the 

 median and oblique dorsal muscles do not occur, there is no 

 underlying apophysis and, therefore, no cushion of muscles 



9 



ventral to VIII, and no lateral longitudinal muscle extending 

 posteriorly ; there is no division into anterior and posterior 

 groups of the latero- and medio-pedal muscles ; the antero- 

 oblique muscles are very large, the postero-oblique almost 

 wanting. An additional horizontal longitudinal muscle either 

 side of the median line at the level of the narrowest part of 

 the foot is present, and above this level, among the latero- 

 pedal fibres and outside of them, are attached to the shell 

 oblique fibres (representing the posterior antero-oblique mus- 

 cle). The usual mantle muscles occur in every part of the 

 mantle around this shell. 



Shell II. 



The region under I and part of II is anterior to the foot 

 proper, and on the ventral surface, in the place of the foot, is 

 the head-fold (with the mouth and circular lip). 



Under II, the median dorsal muscle is crowded into a small 

 space in the median line, and its fibres do not reach the an- 

 terior portion of the shell; the fibres of the oblique dorsal 

 muscles are broken up into groups at their anterior ends. The 

 anterior group of pedal muscles is posterior to its usual posi- 

 tion, and in this group, the anterior portion of the attachment 

 of the medio-pedal and of the postero-oblique are cut off by 

 the oblique radula muscle, joined by the lateral protractor. 

 Antero-oblique muscles are not found anterior to III. The 

 interior mantle muscle is interrupted for a short distance by 

 the lateral protractor. 



