ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA 1 6/ 



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 Euribia, the change 

 in form is such as would be produced by a lateral expansion of the 

 foot. Behind the mouth is the wide metapodium, and on each side of it 

 are the broad epipodia continuous with the metapodium. About mid- 

 wa\' between the mouth and their margin the epipodia carry a small 

 triangular lobe {ins), which evidently represents one-half of the meso- 

 podium ; 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 Euribia. Two minute papillje, the rudiments of 

 the eyes, are placed upon the dorsal surface just behind the anterior 

 edge of the alae [i). 



The oesophagus takes a straight course backwards from the mouth, 

 which contains a minute lingual prominence, and widens gradually 

 into a pyriform muscular gizzard, which is provided with \.\\'o strong 

 curved and conical teeth. The intestine passes from the narrow 

 pylorus, and preserving the same width throughout, bends downwards 

 towards the ventral side, and ultimately terminates in the cavity of the 

 mantle a little to the left of the mesial line, fig. 6. 



Just behind the pylorus a very long straight caecum is given off 

 and sometimes there is a short one in addition by the side of it. The 

 parietes of these sacs are glandular. 



A long " columellar " muscle attaches the animal near to the apex 

 of its shell, and then passes down into the foot, where it spreads 

 out. 



The position of the heart varies remarkably in this genus, and this 

 variation is still more remarkable, if, with Eydoux and Souleyet, we 

 consider it to be one with Cleodora. 



In C. aciculata (figs. 6, 7) the mantle-cavity extends considerably 

 beyond the transversely-barred portion of the mantle, and the base of 

 the auricle abuts upon its lower posterior portion. The apex of the 

 heart points backwards and a little to the left side, and in M. Milne- 

 Edwards's arrangement the animal would be prosobranchiate. In 

 C. virgulata (E. and S.) the base of the auricle lies behind the right 

 posterior portion of the mantle-cavity, and the apex of the ventricle 

 points directly to the left ; it is therefore neither prosobranchiate nor 

 opisthobranchiate. 



In Cleodora curvata, on the other hand, as will be seen immediately, 

 the base of the auricle is posterior and the ventricle points forwards ; 

 it is opisthobranchiate, figs. 4 and 5. 



