272 MR. R. OWEN ON THE ANATOMY OF CLAVAGELLA. 
in Figg. 11 & 12: the great adductor is marked f. Their chief peculiarity is their 
powerful development in so small a Bivalve. 
The digestive system of Clavagella accords with the structure of the same part in 
other Acephalous Mollusks. The mouth! is a transverse slit, the upper and lower labial 
boundaries of which are continued in the form of two transversely striated pointed ten- 
tacula? on either side: each of these prehensile, sensitive, and probably respiratory 
organs measures 6 lines in length and about 1+ line in breadth. No masticatory or 
salivary organs are connected with the mouth ; the esophagus, after a course of 2 lines, 
dilates into a stomach3, the sides of which are perforated by the large hepatic ducts. 
The intestine, after a course of 8 lines, forms a small cecum‘ about | line in length: 
this may be the rudiment of a pancreas; or perhaps is the analogue of the blind sac 
containing the peculiar amber-coloured style, which projects into the pyloric end of the 
stomach of some Bivalves. The little cecum here contained the same brown granular 
material as distended the rest of the canal. The intestine, after making three close 
turns upon itself in the mass of ova and hepatic follicles at the base of the foot, passes 
in immediate contact with, but not through, the heart, and then below the posterior ad- 
ductor, to opposite the posterior orifice of the anal tube. The exterior of the intestine 
has an irregular honeycombed appearance, from the close adhesion to it of the capsules 
of the ova. The liver® has the same divided follicular structure and green colour as in 
other Bivalves. 
The gills have the same laminated structure as in other Bivalves ; they are broad and 
short, corresponding to the form of the animal; and the /amine are arranged in three 
layers instead of two on either side the foot. 
These rows of lamine are not thin compressed layers, but are broad, and project little 
from the sides of the visceral mass. They commence at the sides of the mouth, between 
the labial appendages, and extend backwards towards the inner orifice of the respira- 
tory tube, where they meet, join, and terminate in a point, which is unattached for 
about one eighteenth part of the entire gill) The branchial veins are continued from 
the concave side of the gills, a few lines behind their anterior extremities: these veins 
are joined by others from the muscular part of the mantle, and then terminate in two 
large membranous dark-coloured auricles. These communicate with a fusiform ven- 
tricle, single externally, but divided within, by a longitudinal septum, into two com- 
partments, corresponding to the auricles ; which compartments communicate together 
at the apex of the ventricle, from which the principal artery is continued. 
A large and conspicuous nervous ganglion is situated at the posterior part of the base 
of the foot, just above the orifice of the anal tube. Two nervous cords extend from 
this ganglion on either side the foot to the mouth: other branches radiate in the oppo- 
site direction to the siphonic and adductor muscles. 
' o. Fig. 16. 2 n. Figg. 11, 12, 13, 14, 16. Sq. Fig. 16. 
a7) Bip. 16; 5 w. Fig. 16. 
a 
