114 Proceedings of the Asiatic Society. | May, 
stomus is similar, paucispiral, but testaceous, while it is horny in 
Littorina. Cremnoconchus, however, having occasionally a testaceous 
operculum, indicates a link between the two genera and it also inclines 
to the latter by the males not possessing an appendage to the penis. 
The gills of some Littorine, and particularly those of Cremnoconchus, 
equally indicate a passage to the form of the lungs of true PULMONATA. 
Further, the foot is grooved along the middle of the sole in 
Littorine, it is equally so in the Cycelostomi, only the two parts 
of the sole are in the latter genus still more developed on account of 
the arboreal habitat of the species, though very probably this will not 
be found to be so much the case in the purely terrestrial ones, and in 
Cyclophorus and others the groove has entirely disappeared. The Z#- 
torine have no jaw, at least none distinctly developed, neither have 
the Cyclostomi, but the Cyclophor’, which may be said to be more 
terrestrial, than the former, possess a well-developed jaw, like the 
Heticip# and other puLMONATA. 
Considering these numerous points of structure which I have 
just noticed, it can be scarcely doubted that there exists an inti- 
mate relation between Littoring and Cyclostomt and their associates 3 
and that the origin of the latter may be looked for in the explana 
tion of certain slight changes in the organisation of the former. 
Cremnoconchus, as already stated, shews in several points a still 
greater inclination to Cyclostomus, than do the common Littorine. 
Mr. Blanford’s general remarks* on this subject were, therefore, 
perfectly justified, though he was not in possession of all the details 
upon which he might have been able to base more definite conclu- 
sions. . 
In point of general classification, the comparison of the ana- 
tomy of Littorine and Cyclostomi indicates, that among the dif- 
ferent organs, the structure of the breathing organ seems to 
be subjected to a greater variation, or change, than are for 
instance the generative or, digestive parts, or the radula, &e, 
Therefore, 2 7s not advisable to use the breathing organ as an important 
character in the principal classification of the Lollusca, in the way 
in which it has been introduced for such a purpose in the systems of 
Cuvier and others, 
I could quote other examples in support of this view, as for 
instance that of Cerithidea obtusa, where the gills have entirely 
disappeared, and become replaced by true lungs, while no one 
