CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 493 
Gymnosomata. I thus have been induced to extend to the 
cephalic appendages of the gymnosomatous Pteropoda a work 
specially undertaken to make known the structure of the 
cepbaloconi of Clione. 
This paper is divided into three parts, corresponding to the 
different genera which I have studied: Clione, Clionopsis, 
and Pneumodermon. 
I. Clione . 1 
Clione (PI. XXXV, figs. 1 — 4) possesses two kinds of 
cephalic appendages : 
1. Tentacles properly so called. 
2. Cepbaloconi or buccal cones. 
I shall examine successively these two orders of appen- 
dages. 
a. Tentacles properly so called. 
Clione possesses two pairs of them — an anterior or labial 
pair, and a posterior or nuchal pair. 
Anterior Pair. — It is situated on a hood, whose two 
halves, right and left, may fall back laterally, or be joined to- 
gether again on the antero-posterior mesial line, and hide the 
buccal opening and the three pairs of buccal cones. These 
tentacles are long and retractile. They are not absolutely 
anterior, as in the figure of Eschricht, which represents them 
as equally distant from the dorsal and ventral faces ; 2 they are 
situated nearer the dorsal than to the ventral face, as shown in 
Plate XXXV, fig. 2. 
Very powerful longitudinal muscles occupy the whole of the 
interior part of these appendages; externally, we find a thin 
layer of annular muscular fibres. The epithelium is like that 
of the other parts of the body ; their cells are cylindrical and 
provided with a large nucleus. 
Sections which pass towards the free extremity of these ten- 
tacles show a rather large number of nervous cells, but I have 
1 The species studied is Cl. limacina, Phipps, = Cl. borealis, Pallas. 
2 Eschricht, loc. cit., Taf. 2, fig. 10. 
