57 



ones are of the same size, somewhat smaller than the median [p. v). The lateral visceral 

 ganglia (fig. 97, v) are not in any way connected with the pedal ganglia, but with the cerebral 

 ones. So the central nervous system is quite symmetrical. The distribution of the nerves 

 is the following : 



From the anterior part of each cerebral ganglion three nerves proceed (fig. 97 — 98, 6 — 8). 

 A slight sinuosity, already observed by Pelseneer, divides the ganglion into two segments; from 

 the dorsal segment the tentacular nerve arises (6); the two other nerves sujjply the proboscis. 



The pedal ganglia give origin to two large nerves (figs. 96 — 97, i), ramifying very 

 widely into the fins, as may be seen in fig. 99. Two of the branches e.Ktend in the ventral lobe 

 of the fin. Besides, from each pedal ganglion is.sues a nerve, directed forward (fio-. 98, 

 9—10); a similar nerve occurs in Ctwierina. I could not make out which part of the animal 

 is innervated by these nerves, (perhaps the retractor muscle of the proboscis). 



From each lateral visceral ganglion a very strong mantle-nerve proceeds (fig. 96, 2 — 3); 

 two nerves innervating the visceral mass, issue from the median visceral ganglion. The stronger 

 of these nerves (5) proceeds from the posterior part of the ganglion, slightly to the left, another, 

 very thin, arises from the right side (5). The implantation of (4) and (5) is the only clearly 

 marked asymmetry in the nervous system. 



The buccal ganglia are closely approximated, but yet distinct. These ganglia, as well 

 as the nerves issuing from them, have already been described and figured by Pelseneer ^). 



Cymbuliopsis Pelseneer. 



Cymbiilia (part.) Auctorum. 

 1872. Corolla Dall, Description of sixty new forms of Molluscs from the West coast of North- 

 America and the North Pacific Ocean, Americ. Journ. of Conch., vol. VII, p. 137. 

 1888. Cymbuliopsis Pelseneer, Chall. Rep., LXV, p. 100. 



The species of Dall is very imperfectly known, and as no figure exists of Corolla 

 spectabilis and its diagnosis, given by Dall, consists only in the negative character of the 

 absence of a shell, it remains doubtful whether the species belongs to Cymbtdiopsis, notwith- 

 standing Dale's assertion (see p. 51). The genus is distinguished from Cymbulia and Gleba by 

 the presence of a shell with a very large cavity and thin walls. The animal ver)- closely resembles 

 Gleba, having a proboscis, free throughout its length, a fin without ventral lobe, and with neither 

 radula nor jaws. As far as I can judge, however, it differs from Glcba by the three verv 

 distinct muscular systems in the fin, and in the absence of the indentations on the fin margin. 

 As only very few species of both these genera are known, it is very probable that other forms, 

 not yet discovered, will link together the two types. 



The discrimination of the species of Cymbuliopsis was no easy task, as the type-specimens 

 have been very imperfectly described, and scarcely any attempt has been made to compare 

 the various species mutually "). 



i) L. s. c, p. 26, pi. IV, fig. 2. 



2) A laudable exception is made by Pelseneer (Chall. Rep., LXV, p. loo — loi). 



SIBOGA-EXPEDITIE LI I. 



