HELICINID A. 21 
Hab. N.W. Guatemaua: in the district Cholhuitz, on the slope of the Volcan de Santa 
Maria, at the plantation Helvetia, on the ground, in the second-growth woods, 
two specimens (0. Séol/). 
This strange genus was for a long time only known from the tropical parts of India 
and Polynesia. One American representative has, however, been recorded ; this was 
found on the island of Trinidad by L. Guppy (cf Am. Journ. Conch. iv. p. 178, 
and vi. p. 308), and referred by him to the Indian D. huttoni, Pfr. I have a specimen 
from Trinidad before me, and find that in D. stolli the riblets are very much stronger 
and less numerous. 
Fam. HELICINIDA. 
The shells of the Helicinide, as their name implies, resemble somewhat those of 
the well-known genus Helix; but they are easily to be distinguished from the great 
majority of the Helices by the central part of the lower face being filled up by a 
shelly callosity instead of being excavated into an umbilicus. Moreover, the presence 
of a shelly operculum (wanting only in Proserpina) and of but one pair of feelers, 
and the position of the eyes at the base (not on the tip) of them, widely separate the 
Helicinide from Helix, as also the internal structure, the individual distinction of the 
sexes, and the quality of the radula (Rhipidoglossata) ; as regards the radula, they agree 
only with the Neritine among all land and freshwater shells, and they seem therefore to 
belong to a peculiar series of Mollusca, ascending from marine life to a terrestrial one 
through Trochus, Nerita, Neritina, Hydrocena, and Helicina. ‘The semicircular form 
of the aperture and of the operculum, and the want of spiral structure in the latter, 
serve to distinguish them from the families Cyclophoride and Cyclostomide (with the 
exception of the genus Lourciera, which does not come within the limits of this work). 
The Helicinide are nearly circumtropical and prominently insular, being wanting 
only in the continent of Africa, but they are extremely scarce in the tropical regions 
of Asia, and here limited to the south-eastern sea-shores (China, Siam, Arakan); and 
they are represented in Europe, with the Azores and the Canary Islands, only by the 
peculiar and rare genus Hydrocena. The islands of the Pacific and those of the Carib- 
bean Sea are their head-quarters ; Cuba, for example, having eighty-three species, and 
Jamaica thirty-one. ‘They extend, however, in North and in South America farther than 
the Cyclostomide; Helicina orbiculata is found alive in Georgia and Tennessee, and also 
postpleiocene in the Mississippi valley, and several species occur in Southern Brazil. 
We know at present about forty species found within Mexico and Central America, 
including some which are doubtfully distinct. ‘They are distributed over the whole 
area in the following manner :— 
