6o8 SAMPSON. [Vol. XL 



Shells I and II. 



Corresponding in distribution with the horizontal longitu- 

 dinal muscle (attached to shell VIII) of the posterior end of the 

 body is an oblique muscle from I (Fig, 7, oy), attached imme- 

 diately anterior to the edge of the apophysis of II ; this 

 muscle and another dorsal to it, attached to the most anterior 

 part of the apophysis of II (perhaps to be regarded as another 

 section of the same muscle), pass together obliquely into the 

 foot itself. Although oblique in direction, the muscle does 

 not correspond with the postero-oblique muscles of the other 

 shells, but, like the horizontal muscle under VIII, is different 

 from anything to be found elsewhere in the animal ; the 

 muscles appear to have corresponding functions at the opposite 

 ends of the body. The oblique muscle under I is attached 

 outside the attachments of certain " dorso-ventral " fibres that 

 appear to correspond to latero-pedal fibres of the other shells ; 

 to this extent, it resembles postero-oblique muscles, but unlike 

 them, it passes into the foot between and not outside of the 

 groups of "dorso-ventral" fibres (Fig. 7, 0\ and dv). Further- 

 more, the oblique muscle is attached to so posterior a part of 

 the shell, that it must belong to a posterior rather than to an 

 anterior group of muscles, and it will be remembered that a 

 postero-oblique muscle is found under the other shells with 

 the anterior group only. Finally, if, as seems probable, this 

 muscle is completed by the oblique muscle attached to II, 

 it differs from all the other muscles of the body, in being 

 attached partly under one shell, partly under another. An 

 oblique muscle passing backwards in the posterior group under 

 the other shells would interfere with the apophysis in the 

 movements of the shells, while the relative positions of the 

 first and second shells appear to be less variable than those of 

 the others ; under all the shells, except I, a space occurs an- 

 terior to the edge of the apophysis. 



