100 CONTRIBUTIONS 



more angular above. Were it not a marine shell, there 

 might be some doubt of the propriety of a separation. 

 This group might be placed in the genus Rissoa, if it were 

 not that the mouth is acutely angular above, and is not 

 thickened into a varix, as that genus is. Captain Brown, 

 in his &quot; Illustrations of the Conchology of Great Britain 

 and Ireland,&quot; establishes a genus (Pyramis), which this 

 perhaps more closely resembles, but judging by the figures 

 (there are no descriptions) I believe there is a generic 

 difference. * 



P. secale. Plate 4. Fig. 79. 



Description. Shell subulate, smooth ; substance of the 

 shell thin ; apex acute ; suture linear ; whorls eight, flat 

 tened ; mouth acutely angular above rounded below, one 



introductory remarks. &quot; On sait que ce genre artificiel renferme un 

 grand nombre d especes heterogenes, differentes par la forme generale, 

 par les habitudes, et meme par le caractere artificiel, tire de la forme de 

 1 ouverture. C est done pour me conformer a ce que a ete fait,&quot; &c. 



* Some time after the observation and note were made upon this genus, 

 I observed in M. Payraudeau s excellent work on the recent shells of 

 Corsica, the description and figure of the Mclania Cambessedesii, No. 234 , 

 which naturally belongs to the genus Pasithea. He says, &quot;j aurais pti 

 creer un genre nouveau pour cette espece qui n est point, comme le 

 vraies Melanies, une coquille fluviatile, mais marine.&quot; After some fur 

 ther observations, he proposes to make a division of the genus Melania 

 for these marine species. I believe it is now universally conceded, that 

 there would be an impropriety in placing in the same genus those ani 

 mals whose habits lead them to breathe salt water with those which 

 breathe fresh water or air alone. When the animal is so organized as to 

 be capable indifferently of breathing both, ns in the migratory fishes, it is 

 a very different matter. 



