MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 41 
parts of the body are continuous with the harder, just as the body of a Polyzoon is 
connected with its cell. 
In some individuals I have observed the posterior extremity of the body to be 
surrounded by two circlets of cilia*. 
The head of the animal is provided with two very large tentacles'f', which carry a 
large process upon the inner side of their base, and rudiments of eyes upon the 
outer. Between the tentacles on the ventral side are two projecting lips with the 
aperture of the mouth between them, fig. 3. 
Behind the mouth there are two lobes, separated by a deep notch ; these are the 
two portions of the mesopodium which had begun to be separated in Clio. Behind 
these, again, there is a single tongue-shaped lobe, the metapodium, which is conti- 
nuous on each side with two elongated and expanded epi podia. 
There are no gills, and the anus opens ventrally upon the left side. 
From this genus, to that called Criseis by Rang, but which Eydoux and Souleyet 
unite with Cleodora, the transition is very easy, figs. 6, 7- 
In these forms there is an elongated conical shell, narrow and straight, or wider 
and slightly curved at its extremity. The body puts one in mind of that of a Cepha- 
lopod, being enveloped in a wide mantle, which is united to the body on the dorsal 
side only (fig. 6). The wall of the mantle is very thick, so that it presents a wide 
aperture always open upon the ventral side. Its free edge is, as it were, cut down 
upon its dorsal side, so that ventrally it is considerably longer. On the right side 
this prolonged portion has a rectangular edge, but upon the left it forms a sort of 
ram’s-horn process:|:. The lower part of the inner surface of the mantle is richly 
ciliated, and is raised into a number of transverse ridges, which must probably be 
considered to be rudimentary gills. 
The head and wings are united with the part of the body covered by the mantle, 
by a narrow' neck ; compared with Eurihia, the change in form is such as would be 
produced by a lateral expansion of the foot. Behind the mouth is the wide metapo- 
dium, and on each side of it are the broad epipodia continuous with the metapodium. 
About midway betw'een the mouth and their margin the epipodia carry a small 
triangular lobe {ms), w'hich evidently represents one-half of the mesopodium ; and 
nearly at the same level, on their anterior edges, they present two small curved and 
pointed processes, the representatives of the large tentacles of Eurihia. Two mdnute 
papillm, the rudiments of the eyes, are placed upon the dorsal surface just behind 
the anterior edge of the alse (/). 
* It is a very interesting fact that Professor Muller has found the larvae of Pneumodermon to be provided 
with similar ciliated bands, Ueber die Entwickelungs-formen, &c. Monatsbericht d. k. Akad. d. Wiss. zu 
Berlin, October 1852. 
t These are called “branchies” by Eydoux and Souleyet (pi. 15.), but why I cannot divine, since these 
organs are certainly homologous with the tentacles of Cleodora. 
I Is this to be compared with the small posterior curved process of the edge of the mantle in Gasteropteron 
