. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. and Mascarene Land-Shells. 341 mine to which genus a shell should be referred. The former is almost invariably, I believe, estuarine, living between tide- marks at or near the mouths of rivers, its favourite habitat being the mud of tropical deltas ; while Realia is a land-shell. Assiminea has lately been classed by Dr. Stimpson amongst the Rissoidae, on account of the characters of its lingual denti- tion ; and, whether this character alone is quite sufficient con- nexion or
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. and Mascarene Land-Shells. 341 mine to which genus a shell should be referred. The former is almost invariably, I believe, estuarine, living between tide- marks at or near the mouths of rivers, its favourite habitat being the mud of tropical deltas ; while Realia is a land-shell. Assiminea has lately been classed by Dr. Stimpson amongst the Rissoidae, on account of the characters of its lingual denti- tion ; and, whether this character alone is quite sufficient con- nexion or not, there can be very little doubt that Assiminea^ Truncatella, Bithynia, Tomichia, and probably Acicula, with some other genera, form a very natural group, very nearly allied to Rissoa. As the only known external characters by which Assiminea and Realia can be distinguished are the relative position of the eyes and the form of the tentacles, and as the relations of Realia to the other operculated land-shells are somewhat obscure, it appeared to me very desirable to examine the lingual ribbon ; and as I have been lately furnished, by the kindness of my friend Mr. Geoffroy Nevill, with specimens of R. rubens, Quoy and Gaim., and R. ylobosa, Bens.,both from the Mauritius, with the animal dried inside, I have extracted the tongues, and ascertained that the teeth are of peculiar form, tamioglossate, of course, but differing considerably from those of any Gas- teropod previously examined. The basal denticles on the central teeth, which Dr. Stimpson considers characteristic of the Rissoidaj, are entirely wanting. In the accompanying sketch the teeth of Realia rubens are represented considerably further apart than they occur on the. Lingual teeth of Realia rubens, Quoy & Gaim. lingual ribbon, on which they are so much crowded together that they cannot be clearly made out. The central tooth somewhat resembles that of some Cyclophorida3 in form; it has nine denticulations along the
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