CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEEOPODA. 501 
I have studied the nuchal tentacles were extended and very 
easily visible. Their structure is that of the nuchal tentacles 
of Clione. The eyes are not situated near the tentacles, as 
Troschel says, 1 but on their top. 
Clionopsis does not possess any other cephalic appendages. 
The lips open into a narrow buccal cavity, and do not form a 
hood which can fall back, as with Clione. 
III. Pneumodermon . 2 
Pneumodermon is provided with two kinds of cephalic 
appendages : 
1. Tentacles properly so called, corresponding to those of 
Clione and Clionopsis. 
2. Two acetabuliferous buccal appendages, characteristic of 
the genus (figs. 8, 9). 
a. Tentacles properly so called. 
Like Clione and Clionopsis, Pneumodermon pos- 
sesses two pairs of tentacles, a labial pair and a nuchal pair. 
As with the two preceding genera, the labial tentacles are 
found situated on the two sides of the mouth, rather dor- 
sally. 3 
The nuchal pair has already been described by Souleyet. 4 
Gegenbaur asserts that the first pair is the only one which 
exists. 6 The second pair is, indeed, very difficult to see, 
being retracted in the preserved specimens, the recesses which 
result from it being imperceptible ; however, this place is less 
coloured than the adjacent parts. By making some trans- 
versal sections in the anterior part of Pneumodermon, I 
1 Troschel, loc. cit., pi. x, fig. 9, o. 
The species which I studied are : Pneumodermon mediterraneum, 
van Ben., and P. Peronii, Lam. 
3 Figure 7 may be applied to Pneumodermon as well as to Clionopsis. 
Besides Souleyet (‘ Zoologie du voyage de la Bonite,’ pi. xv, fig. 15) has 
already very well represented this aspect of Pneumodermon. 
* Loc. cit., vol. ii, p. 256, and pi. xv, fig. 14. 
* Gegenbaur, loc. cit., p. 24. 
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