MOLLUSCA OF British Guiana. 39 



strata of the sedimentary rocks furnish often most valu- 

 able confirmatory evidence for the stratigraphical 

 arrangement of the rock formations ; while in many of 

 the calcareous formations, the remains of shells form an 

 appreciable amount of the rock. At the present day, 

 too, the distribution of the land and freshwater Mollusca, 

 especially in insular areas, lends a not inconsiderable 

 amount of assistance in determining the relation of the 

 land areas in former ages. 



The land and freshwater Mollusca of British Guiana, 

 when compared with those occurring in close-lying 

 distrifts, are, so far as they are known, few in number; but 

 this is certainly largely due to the want of investigation, 

 for with the exception of the list, given in Schomburgk'S 

 " Reisen in Britisch Guiana," of the 22 species met with by 

 him during his travels, there has been no serious attempt 

 to throw light upon this branch of Natural History. 

 Lately, from specimens of 24 species which have been 

 collefled for the British Guiana Museum, it has been 

 possible to extend the list of our forms, since but two 

 (Melania atra and Anodonta ensiformis) out of the 24, 

 are certainly identical with species obtained by SCHOM- 

 BURGK ; and more than seven other genera are now 

 for the first time recorded from the colony. It has not 

 been possible in the present communication, in the 

 absence of specimens and suitable books, to give a revision 

 of the species mentioned by SCHOMBURGK; but the 

 following list of recently identified species is given as a 

 basis for future work. With the exception of the testi- 

 ferous slug, and an additional species of Bulimus, the 

 specimens have all been identified by Mr. EDGAR Smith, 

 F.Z.S., etc., etc., Conchologist of the British Museum of 



