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 upper margin, that in the 

 middle being larger than the others. The first lateral tooth 

 has eight denticulations ; the second, which is somewhat like 

 that of Paludina, has six. The outermost lateral tooth exhi- 

 bits the peculiar character of the divisions between the dif- 

 ferent denticulations (twenty in number) being carried down 

 for some distance below the upper margin. This character-, I 

 believe, has only been observed before in West-Indian forms 

 of Cyclostomidse. The tongue of Realia (Omphalotrojns) 

 Ann. & Mag. N. Hist. Ser. 4. Vol. iii. 26 



