20 ZOOLOGICAL GEOGRAPHY. [part hi 



States. Important and characteristic genera are, Glandina, 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 Aciculidee are mostly Antillean, 

 two genera being peculiar there, and one, Truncatella, 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 Licinidae) to the Antilles only. Of these peculiar genera 

 Cistula and Chondropoma are the most important, ranging over 

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

 Cyclotus and Megalomastoma ; while Gydopliorus also occurs all 

 over the region. The Helicinidse are mostly Neotropical, six 

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

 8toastoma, is one of the largest genera; and, with Trochatella 

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

 nelicina 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 

 stiU 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 



