170 J. E. S. MOORE. 



lating in every detail that of Lamellaria perspicua, as 

 figured and described by Bouvier^ and Haller. 



The cerebral ganglia are united by a short but distinct 

 commissure, and are almost completely fused with the pleural 

 ganglia (PI. 18, fig. 5, b.). The right pleural ganglion gives 

 rise to a nerve-cord which passes upwards and directly across 

 the axis of the animal's body. It almost immediately expands 

 into a ganglionic mass, which represents the supra-intestinal 

 ganglion (PL 18, fig. 5, Sup. int. g.). 



This ganglion is in turn connected with the left pleural by 

 the commissure (PI. 18, fig. 5, a. x.). Tlie nervous system is 

 therefore completely zygoneurous on the left. From the left 

 pleural ganglion a nerve-cord passes almost parallel to and 

 below the supra-intestinal commissure to a ganglionic enlarge- 

 ment which represents the subintestiiial ganglion on the 

 right (PI. 18, fig. 5 b, Sb. int.g.). This ganglion is in direct 

 connection with the right pleural ganglion by the connective x'. 

 The nervous system is therefore completely zygoneurous on 

 both sides. All these details could be made out by dissection 

 alone, but the animals were so small that for confirmation I 

 was obliged to resort to sections. 



In all essential details the nervous system just described 

 corresponds with that of Lamellaria, and as the modifications 

 it presents are most complete and peculiar, there can be no 

 doubt that the nervous system of S. zonata offers a true indi- 

 cation of the naticoid affinities of this form. 



The reproductive apparatus very much resembles that of 

 Littorina, the genital gland occupies the upper part of the 

 apical body-whorl, and in the male is related to a simple vas 

 deferens which opens at the extreme upper end of the mantle 

 cavity (PL 18, fig. 2). This opening is, however, prolonged 

 as a ditch or groove (PL 18, fig. 3, g. v.), which is overhung by 

 a flap, which latter structure terminates at the more usual 

 position of the genital opening. 



An exactly similar state of affairs is present in Littorina 

 (PL 15, fig. 1, g. v.), and I found it also very well defined in 

 > ' Ann. (Jes Sciences Nat.,' Series 1, " Zoolog.," torn, iii. 



