XI 



CENTRAL AMERICA 



353 



extending from the political boundary of Mexico in the north 

 to the isthmus of Panama in the south. It thus impinges on 

 three important districts — the N. American, West Indian, and S. 

 American; and it appears, as we should perhaps expect, that the 

 two latter of these regions have considerably more influence 

 upon its fauna than the former. Of the N. American Helicidae, 

 Polygyra is abundant in Mexico only, and two species of SU^ohila 

 reach N. Guatemala, while the Californian Arionta occurs in 

 Mexico. S. American Helicidae, in the sub-genera Solar opsis 

 and Labyrinthus^ occur no farther north than Costa Rica. Not 

 a single representative of any of the characteristic West Indian 

 Helicidae occurs. BuUmulus and Otostomus, which form so large 

 a proportion of the Mollusca of Venezuela, Colombia, Ecuador, and 

 Peru, together with OrtJialicus^ are abundant all over the region. 

 Again, Cylindrella^ Macroceramus^ and some of the characteristic 

 Antillean operculates, are represented, their occurrence being in 

 most cases limited to the eastern coast-line and eastern slope of 

 the central range. 



Besides these external elements, the region is rich in indigenous 

 genera. Central America is remarkable 

 for an immense number of large carni- 

 vorous Mollusca possessing shells. There 

 are 49 species of Grlandina^ the bulk of 

 which occur in eastern and southern 

 Mexico; 36 of Streptostyla (S.E. Mexico 

 and Guatemala, only 1 species reaching 

 Venezuela and another Peru) ; 5 of Sala- 

 siella, 2 of Petenia^ and 1 of Strehelia; the 

 last three genera being peculiar. Strept- 

 axis, fairly common in S. America, does 

 not occur. Velifera and Cryptostracon, 

 two remarkable slug-like forms, each with 

 a single species, are peculiar to Costa Rica. 

 Among the especial peculiarities of the 

 region are the giant forms belonging to the 

 Cylindrellidae, which are known as ITolo- 

 spira, Eucalodium^ and Coelocentrum (Fig. 

 232). They are almost entirely peculiar 

 to Mexico, only 7 out of a total of 33 reaching south of that 

 district, and only 1 not occurring in it at all. 



VOL. HI 2 A 



Fig. 232.— Examples of 

 characteristic Mexican 

 Mollusca: A, Coelocen- 

 trum turris Pfr.; B, 

 Streptostyla Delattrei 

 Pfr. 



