MEXICAN REGION 



401 



tory and Oregon( De Kay.) Limncea, umbrosa, Say? and Planorbis-corpulodus 

 Say, are found in the Columbia R. 



20. INIextcan Region. 

 The lowlands of the northern half of Tropical America constitute only one 

 botanical region, extending from the R. Grande del Norte to the Amazon ; 

 but on zoological grounds it may be divided into two smaller areas. The 

 Mexican province, including Central America, itself comprises three jjhysical 

 regions ; the comparatively rainless and treeless districts of the west ; the 

 mountains or high table-lands with their peculiar flora ; and the rainy wooded 

 region that borders the Caribbean Sea. The land snails of Central America 

 resemble those of the Antilles in the prevalence of some characteristic 

 ^enev^—G/andma, Cylmdre/Za and Ee/ici7ia,—oi v^-'hkh very few species are 

 found on the northern Coast of the Gulf of Mexico 

 rous but chiefl)- thin, translucent species. 



Helix 33 Glandina 25 



Proserpina 1 Toroatellina 



The Bidimi are nume- 



Bulimus 



Succiuea 



Achatina (Spiraxis) 



... 1 



30 Pupa 1 



6 Cylindrella 11 



12 Cyclotus 1 



Cistula 7 



Cyclophorus 3 



Chondropoma 3 



IMegaloma 2 



Helicina 22 



Amongst the fresh-water shells are Neritina picfa, Cyclas macula'a. Cor- 

 h'lcida convexa, and 7 species of Cyrena. From jNJazatlan, Mr. Carpenter 

 describes Cyrena oUvacea and Mexicnna, GnatJiodon trigonus, Anodon 

 cicouia (allied to the Brazilian A. anserina), PJiysa mirantta and elata, Tla- 

 norh'is sp. Melampus olioaceus. Two brackish-water species, Ceritliidlum 

 varicosum and Montagnei — are common to S. America. 



21. Antilles. 



The West Indian Islands have supplied nearly 500 species oiHeJicid(P, a 

 larger number than any province except the Lusitanian ; and above 260 Cy- 

 clostomidce, or nearly 3 times as many as India. They are also richest in 

 generic forms, and the climate is highly favourable to the multiplication of 

 individuals. The mean temp, of the Antilles is 59°— 78°, and the annual 

 fall of rain exceeds 100 inches in most of the islands. 



Helix 200 



Stenopus 2 



Sagda 20 



Proserpina 6 



Bulimus 53 



Achatina 27 



Glandiua 40 



Spiraxis 9 



Toruatellina 1 



Pupa 26 



Cylindrella 73 



Clausilia 1 



Balea 1 



Succinea , 16 



Chondropoma 15 



Choanopoma 53 



Adamsiella 10 



Cistula 36 



Cyclophorus 1 



Cyclotus 14 



Megaloma 8 



Helicina 



Alcatlia 



Trochatella 

 Lucidella . , 

 Stoastoma . . 

 Geomelania 



Probably every island has some peculiar species, and those of the great 

 islands, like Cuba and Jamaica are nearly all distinct. To Jamaica belong 



