20 
ZOOLOGICAL GEOGRAPHY. 
[PART III. 
States. Important and characteristic genera are, Qlandina , in 
all the tropical parts of the region; Gylindrdla, in Central 
America and the Antilles ; Bulimus, containing many large and 
handsome species in South America ; Stenogyra, widely spread in 
the tropics ; and Streptaxis, in Tropical South America. 
Among the Operculata, the Aciculidse are mostly Antillean, 
two genera being peculiar there, and one, Trunccitella, of wide 
distribution, but most abundant in the West Indian Islands. 
The Cyclostomidge are represented by 15 genera, 9 being 
peculiar to the region, and 5 of these (belonging to the sub- 
family Licinidae) to the Antilles only. Of these peculiar genera 
Cistula and Chondropoma are the most important, ranging oyer 
all the tropical parts of the region. Other important genera are 
Cyclotus and Megalomastoma ; while CydopJiorus also occurs all 
over the region. The Helicinidse are mostly Neotropical, six 
out of the seven genera being found here, and four are peculiar. 
Stoastoma , is one of the largest genera; and, with Trockatella 
and Alcadia, is confined to the Antilles, while the wide-spread 
Helicina is most abundant there. 
The Limacidse, or Old World slugs, are absent from the region, 
their place being taken by the allied family, Oncidiadse. 
Marine Shells. — We go out of our usual course to say a few 
words about the marine shells of this region, because their 
distribution on the two sides of the continent is important, as 
an indication of the former separation of North and South 
America, and the connection of the Atlantic and Pacific Oceans. 
It was once thought that no species of shells were common to 
the two sides of the Central American Isthmus, and Dr. Morch 
still holds that opinion; but Dr. Philip Carpenter, who has 
paid special attention to the subject, considers that there are at 
least 35 species absolutely identical, while as many others are 
so close that they may be only varieties. Nearly 70 others are 
distinct but representative species. The genera of marine mol- 
lusca are very largely common to the east and west coasts, 
more than 40 being so named in the lists published by Mr. 
Woodward. The West Indian Islands being a rich shell dis- 
trict, produce a number of peculiar forms, and the west coast of 
