G. A. DKEW ON YOLDIA LIMATULA, SAY. 7 



This dirt is swept back over the expansions and so out of the cavity. 

 The rich nervous supply comes as branches of the posterior pallial 

 nerves. 



Anterior projections of the mantle. The antero-ventral margins of 

 the mantle may be protruded a short distance beyond the margin of 

 the shell, Fig. 1, and seem to aid in cleaning the foot when it is 

 being withdrawn from the mud. These margins are destitute of 

 tentacles, but they are well supplied with sense-papillae. 



Arising from each margin, opposite the extremity of the stripe on 

 the anterior end of the shell, is an oblong projection, Fig. 1, ae. This 

 projection carries a row of sense-papillae, and is ciliated on either side, 

 Figs. 16 and 17. Branches of the anterior pallial nerve undoubtedly 

 enter it, and enlarged pallial muscles act as its retractor. 



These organs are very sensitive to mechanical stimulation, and 

 probably serve as tactile organs, but their function is not known. 

 They are placed so near the edges of the retracted foot that it seems 

 possible that they may serve some function in connection with it, 

 but no observations were made that support this surmise or that give 

 a clue to any other function. 



FOOT. 

 FIGURES 3, 5 AND 9, f. 



The foot, Fig. 3, f., is very large and powerful. Its sides form 

 two muscular flaps, that lie side by side, and are capable of being 

 extended laterally, Fig. 9, in which position they form an almost flat or 

 arched surface. It is this part of the foot that is called the sole. 



Notwithstanding its being a rigid muscular organ, known to be 

 adapted for burrowing 5 aDd 16 and executing movements with remark- 

 able rapidity, 1 and 17 this part of the foot is still referred to as a " creeping 

 sole.' 1 * 



The free margins of the flaps are thin, and are fringed with 

 flattened papillas that are very sensitive to touch. There are four 

 pairs of foot-muscles, one posterior and three anterior. The posterior 

 foot-muscles, Fig. 3, pfm., are inserted on the shell, just in front of 

 the posterior adductor muscle and very near the bases of the teeth. 

 They are very large and send all of their fibres forward, along the 



*See note on page 9 of the paper. 



