6i6 SAMPSON. [Vol. XL 



extended laterally on either side, dorsal to the cartilages (cf. 

 Figs. 7, 9, II, rs)\ a pair of glands opens into the oesophagus 

 at a point posterior to these lateral projections (see Fig. lo^gl). 



The names used for the muscles in the following descrip- 

 tion indicate in most cases the position and directions of the 

 muscles rather than their function, as that is not understood; 

 the plan is that adopted by Geddes, and in cases where the 

 muscles in Chiton appear to correspond with those in the forms 

 described by him, I have used the same lettering. 



The muscles pass from the radula sheath to the cartilage {nis\ 

 and msz of figures) ; from the shells to the cartilage {pr, cr, 

 and Iproi figures), or to the radula sheath (^;'and ^rof figures); 

 from the muscular head-fold or foot to the cartilage i^pr, al, pi 

 of figures); and in one case from one cartilage to the other (vtr). 



The muscles from the radula sheath to the cartilage are of 

 two kinds: broad, flat muscles from the lateral extension of 

 the radula sheath (Figs. 7, 9, ins\) running posteriorly to the 

 outside of the cartilage (Fig. 9, 7ns\), and thread-like muscles 

 (approximately circular in cross-section. Figs. 11, 12, msz), 

 running from the part of the radula sheath that immediately 

 surrounds the radula (Fig. 9, msz), posteriorly, to be attached 

 to the inner and dorsal surface of the cartilage (;;W2, posterior 

 to Fig. 10); these thread-like muscles are attached to the car- 

 tilage more posteriorly than the broad muscles, and so cover 

 them dorsally posterior to the lateral projection of the radula 

 sheath (Fig. 11, msz). 



The horizontal muscles ("protractors") that are attached in 

 two groups on either side to the anterior part of shell I, and 

 pass between the groups of dorso-ventral fibres (as described 

 in the account of the muscles to the head-fold under I), unite 

 posteriorly into one group, and then pass to the outside of the 

 cartilage, to be attached to it posterior to the attachment of 

 the broad muscles {ms\) of the sheath {cf. Figs. 7, 9, 10, 11, 

 pf). A pair of muscles (Fig. 11, <:r), attached to I at a point 

 almost as anterior as the attachments of the protractors, cross 

 in the middle line, and pass with the protractors to the car- 

 tilages (Fig. 9, cr), but are attached to the cartilage anterior 

 to the broad sheath muscles {ms\). 



