74 H. HEATH and M. H. SPAULDING, 



fashion the larger pedal nerve supplies the lateral and posterior 

 portions of the foot. 



A short distance beyond the origin of the larger pedal nerve (j)^) 

 a small nerve arises that passes directly outward into the posterior 

 portion of the proboscis to its margin. From some point, usually not 

 far from its origin, this posterior proboscidial nerve gives rise to an 

 exceedingly delicate fibre that connects with one of the more posterior 

 branches of the smaller pedal nerve (p^). Another small nerve (Figs. 4, 

 5 m) arises from the larger of the lateral pedal cords, a short distance 

 beyond its union with the pedal ganglion, and coursing backward 

 enters the pedal ganglion on its posterior border. From it arise 

 three fibres of extreme tenuity which renders it difficult to determine 

 their exact destination. The more anterior branch extends outward 

 as far as the point of union of the proboscis and fin, where it breaks 

 up into a number of subdivisions of which one or two appear to ex- 

 tend out onto the surface of the casque. The more posterior branches 

 originating from this loop (m), proceed ventrally and branching are 

 apparently distributed to the soft gelatinous tissue between the base 

 of the proboscis and the casque. 



Of the palliai nerves arising from the pleural ganglia (pi) the 

 right (Figs. 4, 5 v^) is considerably the larger. Passing outward and 

 backward it then extends forward and downward until it reaches the 

 postero-lateral border of the palliai gland (Fig. 9). Skirting this for 

 a considerable distance it enters the elongated osphradium. At about 

 equidistant intervals between its origin and the osphradium this nerve 

 gives 0Ö' three or four branches that extend over the surface of the 

 casque. The left palUal nerve (Figs. 4, 5, 9 v^) courses backward 

 and gradually rising toward the dorsal surface of the animal comes 

 cleaily into view at the posterior limits of the proboscis. A short 

 distance out from the pleural ganglion it gives rise to a large nerve, 

 and one usually difficult to follow in this part of its course owing to 

 several small muscle fibres and wrinkles that are almost invariably 

 present in the skin in this region. In carefully cleared preparations, 

 however, it may be traced outward and after giving ofi" one or two 

 branches that extend over the surface of the shell it passes forward 

 and likewise innervates the skin over the anterior portions of the 

 casque. The posterior branch divides into several delicate fibres that 

 extend to the hinder extremity of the animal and after bending on 

 to the ventral surface may be followed to about the level of the 

 hinder border of the palliai gland. In the rnost favorable preparations 



