6o6 SAMPSON. [Vol. XI. 



shell) and are limited posteriorly by a muscle of the mantle 

 around the end of the body. An anterior antero-oblique muscle 

 is well defined. At the level of the narrowest part of the foot, 

 within the latero-pedal muscle and hence bounding the body 

 cavity, is a powerful horizontal longitudinal muscle that is 

 attached to the shell (Fig. 13, VIII, hi) as it forms the dorsal 

 curvature of the end of the body, and extends anteriorly into 

 the foot : its attachment to the shell reaches the median line, 

 and thus the muscle meets its fellow of the opposite side of 

 the body, over the union of the branchio-visceral nerves. At 

 a higher level than the horizontal muscle, fibres are attached 

 to the shell among and outside the fibres of the latero-pedal 

 muscle (Fig. 13, VIII, ad) and pass anteriorly and slightly 

 obliquely into the foot, taking the place of the antero-oblique 

 muscle in the posterior part of the shell. 



Shell II. 



Under II a condition the reverse of that under VIII, at the 

 opposite end of the body, is found among the oblique muscles, 

 since the postero-oblique is very prominent and antero-oblique 

 fibres are wanting ; the antero-oblique were seen to have 

 diminished already under III, where the muscle of that direc- 

 tion in the anterior group is so reduced as to be no longer 

 recognizable as a distinct muscle when the fibres have passed 

 anteriorly under II. 



The attachments of the fibres of the oblique dorsal shell 

 muscle are in groups among the latero-pedal fibres of the 

 anterior group, and some of the oblique dorsal fibres reach- so 

 far laterally as to interrupt the posterior part of the attachment 

 of the postero-oblique {cf. Fig. 3 and Fig. 13, II). 



Some of the attachments of the muscles of the anterior 

 group are interrupted also by muscles to the buccal mass, and 

 the relations of their anterior limits altered : a large radula 

 muscle (perhaps the " sphincter oris " of Haller), attached far 

 out in the mantle to II (Figs. 10, 9, or, 3, ora), passes obliquely 

 forward to the buccal mass ("oblique radula muscle"). Im- 

 mediately ventral to this muscle where it has reached the 



