124 Dr. J. E. Gray on the Division of Ctenobranchous XIII, — On the Division of Ctenobranchous Gasteropodous Mol-lusca into lai-ger Groups and Families. By J. E. Gray, Ph.D., F.R.S., V.P.Z.S. &c. CuviER, Dumeril, and Lamarck separated the Gasteropodous Mollusca, which have pectinated or comb-like gills, into two di-visions, according as they possessed or were without a siphon to facilitate the admission of water to their gills, probably being influenced by preceding conchologists, who had in a similar manner divided the spiral shells into those which had an entire, or an emarginated, or a channelled mouth. Lamarck called those with a siphon Zoophaga, and those without it Phyto-phaga, believing the food of the molluscs to be indicated by the form of the mantle. As we have become moi'e acquainted with the habits of the Mollusca, it has been observed that many of the animals without any siphon to the mantle, as Natica, Scalaria, lanthina, &c., are quite as carnivorous as those which have the siphon most perfectly developed ; on the other hand, Lamarck found it requisite to arrange many genera, as Cerithium, Melanopsis, Planaxis, &c., with the Phytophaga with entire mouths, though the animals have as well-developed siphons and the shells as distinct canal or siphonal notch, as any of the genera of Zoophagous Mollusca. These divisions, however, have been almost universally adopted. Dr. Loven in his paper on the Scandinavian Mollusca and on the Tongues of these animals, divided the Gasteropoda into natural families independent of these divisions, and Dr. Troschel in his arrangement of Mol-lusca has followed the same course, separating the families into groups according to the structure of their tongues. The observations which Dr. Troschel made on the arrangement which I published in Mrs. Gray's work, * Figures of Molluscous Animals,' have induced me to reconsider the subject, consult again all the authorities, and examine the tongues of the mol-luscous animals which have been lately received at the Museum collections. Being impressed with the importance which Dr. Loven at-tached to the form of the mouth, I was induced to pay attention to this character, and I believe that it affords a much more na-tural one to separate families into two great groups, than the presence or the absence of the siphon of the mantle, and one which appears to be more consistent with the habits of the animal and much less liable to exceptions. I may observe in passing that some of the French zoologists do not appear to have been impressed with its importance, for MM. Quoy and Gaimard in some few instances erroneously represent some of the species of a geiuis, as a Murex and Terebra, for example, as having a
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