350 



PORTO RICO 



CHAP. 



ill the south-west district of the latter island of Sagcla (2 sp.). 

 The relative numbers of the genera Strophia^ Macroceramus^ and 

 Helicina^ as given below (p. 351), are of interest in this con- 

 nexion. 



Porto Mico, with Vieque, is practically a fragment of San 

 Domingo. The points of close relationship are the occurrence 

 of Caracolus^ Cepolis^ and Parthena among the Helicidae, and of 

 Siynpulopsis^ Pseudobalea^ and Stoastoyna. Cylindrella and Ma- 

 croceramus aie but poorly represented, but Atrophia still occurs. 



Fig. 231. — Examples of West 

 Indian Helices: A, Helix 

 {Parthena) angulata Fer., 

 Porto Rico; B. Helix (The- 

 Uclomus)lima Fe'r., Vieqne; 

 C, Helix {Dentellaria) 7iux 

 denticulata Chem., Martin- 

 ique. 



The land operculates (see the Table) show equal signs of 

 removal from the headquarters of development. Megalomas- 

 toma^ however, has some striking forms. The appearance of a 

 single Claiisilia, whose nearest relations are in the northern 

 Andes, is very remarkable. Gaeotis, which is allied to Peltella 

 (Ecuador only), is peculiar. 



