40 MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 
In truth, the foot, though very small in these genera, is exceedingly well-marked, 
and shows a clear division into mesopodium and metapodium. It may be a matter 
of doubt whether the propodium is developed or not, and this question can be settled 
by embryology alone ; but for the present, I think, it may be fairly presumed that it 
is represented by the tentaculigerous hood of Pneumodermon and by the tentaculige- 
rous lobes of Clio-, following in this case a very common tendency (exempUfied in 
all the Cephalopods and in many Gasteropods) to become developed over and in front 
of the mouth*. 
As Cuvier demonstrated, there is no mantle” in Pneumodermon and a/of ; the 
body of these mollusks answering precisely to that of a Firoloides. 1 he relation of 
the gilUaminse and of the small anomalous shell in Pneumodermon sufficiently cor- 
roborates Cuvier s view. Gills are never placed upon the outer surface of a mantle ; 
and if anything answers to such an organ it must be the small space covered by the 
rudimentary shell, so that the relations of the parts are, in fact, similar in Pneumoder- 
mon to what we find in Firola and Carinaroides. 
Finally, new parts, the ‘‘ alee,” make their appearance in these genera and give its 
character to the order (figs. 1, 2, 3, 4, 7? cp). 
Considering the position and relation of these organs as distinct developments fiom 
the upper part of the sides of the foot, and the fact that their nerves arise, like those 
of the foot, from the pedal ganglia, I propose to consider them as parts of the foot 
and to call them the ‘‘ epipodia.” It has been long since shown by Van Beneden 
and others that they have nothing to do with the respiratory function. 
In this subtype the intestine opens on the right ventral side of the neck, and dis- 
section shows its first bend to be ventral, that is, towards the side of the pedal 
ganglia. 
2. The genus PsycheX or Eurihia offers a very interesting transition from the 
foregoing to the second subtype. This genus is commonly said to have a cartdagi- 
nous shell, but this so-called shell appears, upon careful examination, to be only the 
thickened integument of the body ; it is not secreted by a true mantle, like that of 
Cleodora, &c. The notion of a shell has arisen seemingly from the fact that a sort 
of cleft exists anteriorly from which the locomotive organs of the animal can be pro- 
truded and into which they can be retracted, but at the margin of this cleft the softer 
* The origin of the nerves of the acetabuliferous tentacula may probably throw some light upon this matter ; I 
have not had the opportunity of dissecting sufficiently large specimens of either PH(?Mmo*r»iOK or Clio, carefully, 
with regard to this especial point. From the figures of Eydoux and Souletet. one would be led to believe 
that the nerves of the acetabuliferous tentacles arise from the cephalic ganglia, which would be a very great 
objection to the view advocated above, since ail the other parts of the foot, the mesopodium, metapodium and 
epipodium are supplied by the pedal ganglia. (See Eydoux and Souleyet, plate 15. fig. 30, and plate 15 bis, 
fig. 8.) 
t Eydoux and Souleyet, however, call it “ manteau ” in the description of their figures. Leuckart also 
opposes Cuvier’s view, but I think without reason. (Op. cit. p. 146 note.) 
X My species appears to be the Eurihia Gaudichaudii of Eydoux and Souleyet. 
