MORPHOLOGY OF THE HELICINID^. 787 



with the pleurals that it is unrecognizable as a separate ganglion, 

 even in sections (PL XXXVIII. figs. 45 to 52). The pedal cords, 

 though not so widely separated in any of the species of Heli- 

 cinidse that I have dissected as in the Neritidae, are not so closely 

 approximated as shown in Bouvier's figure. They are fairly 

 close togetlier and nearly parallel to one another in Eutrocluitella 

 pidchella, somewhat more divergent in Alcadia hollandi, further 

 apart in A. palliata, and widely divergent in Aphanoconia 

 andamanica. The actual amount of divergence or approximation 

 is, however, undoubtedly dependent on the degree of contraction 

 of the muscular mass of the foot, and is a character of no great 

 importance. If the foot is much contracted the pedal cords are 

 approximated and the numerous and slender pedal commissures 

 are arched : if the foot is relaxed the cords are further apart and 

 the commissures ai^e pulled out straight. I cannot but think 

 that Bouvier has exaggerated the length of the cerebro-pleural 

 and cerebro-pedal connectives. In none of the sjDecies that I have 

 examined are they appreciably longer than the antero-posterior 

 diameter of the cerebral ganglia, and in some species, e. g. 

 Lucidella aureola, they are very short, but it is, of course, j^ossible 

 that they are unusually long in H. sagraiana. In respect of the 

 nerves issuing from the ganglionic mass formed by the fusion of 

 the anterior ends of the pedal with the pleural centres, Bouvier, 

 while otherwise exact, makes one important omission. He does 

 not figui'e or describe a relatively large pair of nerves which 

 originate one on each side of the most anterior pedal commissurei 

 from the dorsal surface of the swollen anterior ends of the pedal 

 cords. Each of these nerves (PI. XXXIX. figs. 43 & 44, n.op.) 

 passes outwards and backwards, penetrates the muscular wall of 

 the body, and passes to the muscles of the operculum, hence the 

 nerves in question may be called the opei'cular nerves. That of 

 the right side breaks up into a number of fine twigs in the 

 opercular muscles, that of the left side gives oflT a stout branch 

 which passes to a peculiar hollow organ connected with a plate of 

 cartilage near the left corner of the opercular lobe. This organ 

 will be described in detail fui-ther on. 



The otocysts are situated just above the origins of the two 

 opercular nei'ves, and are therefore on the dorsal side of the pedal 

 ganglia, as is shown in fig. 44. Bouvier, describing the otocysts 

 of Helicina brasiliensis says " elles sont situees sous les cordons 

 pedieux " : and it is true that in a retracted specimen, in which 

 the head has been drawn back behind the foot, so that the 

 pedal cords appear to lie in front of the cerebral ganglia, one 

 does find the otocysts below the pedal cords, when making a 

 dissection from the dorsal side. But in such a case the sole of 

 the foot is uppermost, and the morphologically doi'sal side of the 

 pedal cords is turned downwards, this change of position being 

 very puzzling to the observer both in sections and dissections. 

 It is worth remarking in this connection that in my experience 

 the small Polynesian genera, Aphanoconia, Palceohelicina, and, in 



