20 ZOOLOGICAL GEOGRAPHY. [part hi. 



States. Important and cliaracteristic genera are, Qlandina, in 

 all the tropical parts of the region; Cylindrella, 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 Aciculidre are mostly Antillean, 

 tAvo genera being peculiar there, and one, Truncatclla, of wide 

 distribution, but most abundant in the West Indian Islands. 

 The Cyclostomidse are represented by 15 genera, 9 being 

 peculiar to the region, and 5 of these (belonging to the sub- 

 family Licinidie) to the Antilles only. Of these peculiar genera 

 Cistula and Clwnclro'poma are the most important, ranging over 

 all the tropical parts of tlie region. Other important genera are 

 Cydotus and Ileyalomasioma ; while CyclojjJiorus also occurs all 

 over the region. The Helicinidte are mostly Neotropical, six 

 out of the seven genera being found here, and four are peculiar. 

 Stoastoma, is one of the largest genera; and, witli Trochatdla 

 and Alcadia, is confined to the Antilles, while the wide-spread 

 Hdicina is most abundant there. 



The Limacidee, or Old World slugs, are absent from the region, 

 their place being taken by the allied family, Oncidiada?. 



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. IMorch 

 still holds tliat 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 arc 

 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. TJie West Indian Islands being a rich shell dis- 

 trict, produce a number of peculiar forms, and the west coast of 



