32 PROCEEDINGS OF THE SCIENTIFIC ASSOCIATION. 
Neritina Lamarck 1809. 
Fluviatile (rarely marine) Operculata with semiglobose 
rather flattened shells, having a scarcely prominent spire 
and .a semicircular aperture without teeth on the outer lip 
and furnished with a shelly paucispiral operculum having 
a marginal nucleus and an apophysis. 
. This genus is a fluviatile form of the marine genus Neri- 
ta. Two marine species of Neritina are found on the shores 
of Trinidad ; Neritina viridis, commonly known as the 
“ green-pea shell and N meleagris , a species very abun- 
dant in the harbor of. Port-of- Spain and in mangrove 
swamps. This last species resembles our only fluviatile 
species (N. microstoma) ; but it is more varied in color be- 
sides being different in shape, &c. 
Neritina microstoma D’Orbigny. 
JL Orbigny, Moll, de Cuba, pi. xvii, f. 3fl. 
A dark olive-green Neritine marked with black lines 
giving the appearance of scales. It is found at the Gover- 
nor’s Fountain near Port-of-Spain, and I have received 
examples from Moruga and other parts of the island. It 
occurs in Cuba. 
Diameter 14 mill., height 12 mill. 
Order Pectinibranckiata (Tmnioglossata). 
. Ampullaria Lamarck 1799. 
Fluviatile Operculata with globular umbilicated shells 
having a large entire aperture and a short spire, and fur- 
nished with a stout horny suboval operculum having its 
nucleus near its inner margin. 
Ampullaria urceus Muller. 
Nerita urceus, Muller. 
Helix urceus, Dillwgn, Recnt Shells, 918. 
Ampullaria rugosa, Lamarck. 
