REPORT ON THE PTEROPODA. 
51 
anterior commissure arises at the base of the median nerve of the foot. The cervical 
plexus formed by the anastomosis of the cervical nerve and the nerve from the pleural 
ganglion agrees with that of the preceding genera. The pleural ganglia are paired as in 
all Gymnosomata. 
The visceral ganglia resemble those of all the other genera hitherto studied, being 
characterised by the asymmetry of their nerves. 
Eschricht and von Jhering have represented these nerves as symmetrical, and Wagner 
has figured 1 one of them as taking origin between the two ganglia, which is quite 
contrary to fact. 
As a matter of fact, and as Souleyet alone has accurately depicted, though without 
description, only one nerve springs from the right ganglion, whilst three nerves issue 
from the left, — a lateral one, corresponding to the nerve from the right ganglion, and two 
others almost median. 
According to Wagner 2 the lateral nerve of the left ganglion sometimes arises from 
the pedal ganglion ! I have never observed such an arrangement in anyone of the 
numerous specimens of Clione which I have dissected, and it seems to me almost 
impossible. 
The nerve from the right ganglion behaves like the corresponding nerve in other 
Gymnosomata. One of its branches supplies the osphradium, situated between the anus 
and the genital aperture (PL V. fig. 9). The osphradium is circular in form and its 
structure recalls the corresponding organ of the Thecosomata, for it is formed of a mass 
of ganglionic cells, covered by columnar ciliated epithelium (PL Y. fig. 7). 
The buccal ganglia do not present any characters different from those of other genera ; 
the cerebro-buccal connective always arises from the oesophageal face of the cerebral 
ganglia, and never, as in von Jhering’s figure, 3 from their anterior border by a trunk 
common to the cerebral nerves. 
Family IY. Halopsychida 
The specimens which I had the opportunity of studying were not in a condition 
favourable to delicate anatomical investigation. The alcohol had not penetrated well 
through the thick envelop of the body, so that the viscera were badly preserved. 
Hence, as regards a large portion of the visceral anatomy, I have only been able to 
control and confirm the greater part of the brief description of Souleyet, and to rectify 
some of his statements which were incorrect. 
The Head is cylindrical and very small in proportion to the body of the animal. In 
1 Die Wirbellosen des weissen Meeres, Bd. i. pi. xii. figs. 1, 12. 
2 Ibid., p. 100, pi. xi. figs. 4, 11. 
3 Vergleichende Anatomie des Nervensystemes und Phylogenie der Mollusken, pi. v. fig. 20, 1. 
