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 “Tlustrations of the Conchology of Great Britain 
and Ireland,” 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 anguiar above—rounded below, one 
introductory remarks. ‘ On sait que ce genre artificiel renferme un 
grand nombre d’espéces hétérogénes, différentes par la forme générale, 
par les habitudes, et meme par le caractére artificiel, tiré de la forme de 
ouverture. C’est donc pour me conformer a ce que a été fait,” &e. 
* Some time after the observation and note were made upon this genus, 
[ observed in M. Payraudeau’s excellent work on the recent shells of 
Corsica, the description and figure of the Melania Cambessedesit, No. 234, 
which naturally belongs to the genus Pasithea. He says, “‘j’aurais pu 
créer un genre nouveau pour cette espéce qui n’est point, comme les 
vraies Mélanies, une coquille fluviatile, mais marine.’ 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, as inthe migratory fishes, it is 
a very different matter. 
