CASTEKOPODA PECTINI15R ANCHIATA. 363 



Helicina, Lam.(l) 



Judging by the shell, the Helicincc are Ampullariae in which the 

 margin of the aperture is reflected(2). 



When this reflected margin is trenchant, they are the Ampullin^, 

 Blainv. ; and when it is in an obtuse ridge, the Olygir^, Say. 



There is one species which is remarkable for a border and stony 

 traverse, on the internal face of its operculum(3). 



The organs of respiration in these animals are arranged as in the 

 Cyclostomx, and like the latter they can live out of water(4). 



Melania, Lam. 



A thicker shell; the aperture, higher than it is wide, enlarges oppo- 

 site to the spire; the columella without plicae or umbilicus; length of 

 the spire very various. 



The MelaniiE inhabit rivers, but are not found in France, the ani- 

 mal has long tentacula, the eyes being on their external side, and at 

 about the third of their length(5). The 



RissoA, Frcminv. Acmea, Hartm. 



Differs from Melania, because the two edges of the aperture unite 

 above(6). The 



Melanopsis, Feruss., 



Where the form is nearly that of a Melania, differs from it in a 

 callus on the columella, and in a vestige of an emargination near the 



(1) Montfort has changed the name HeUcina into Pltonnilla, but it has not been 

 adopted, and can only be quoted as a synonyme. 



(2) The Hel. striata, Blainv., Malac, xxxv, iv. 



(3) The Hel. neritella. List., LXI, 59, copied Blainv., Malac, xxxix, 2. 



(4) It is from this circumstance that M. de Fenissac has been induced to class 

 this subgenus with that of the Cyclostomx in an order which he names tlie Pul- 

 monea Operculata. See the Monograph of this genus by M. Gray, Zool. Joum., 

 Nos. 1 and 2. 



(5) Mekmie thiarc {Melania amarula, Lam.), Chemn., Tab., 134, f. 1218 and 

 1219; from the Isle of France and Madagascar. 



Add: Mel. truncata. Lam., Encyclop-, pi. 458, f. 3, a b; Mel. coardata. Id., 

 Encyclop., pi. 458, f. 5, a b., and a great many fossil species, among which are, 

 Mel. semi-placata, Defr.; Mel. Cuvieri, Desh., Coq. Foss., des environs de Paris, 

 tome II, pi. xil, f. 1, 2; Mel. constellata, Lara. 



(6) M. de Freminville describes seven species in the Nouv. Bullet, des Sc. 

 Nat. de la Soc. Phil., 1814, p. 7, and M. Audouin, three, in the Descr. de I'Eg.: 

 Riss. Freminvillii, Coq., pi. iii, f. 20; Riss. Desmarestii, lb-, 21; Riss. Orbignii, 

 lb., f. 22. 



