304 AMERICAN JOURNAL 



ON THE TERRESTRIAL MOLLUSCA OF THE GUANO 

 ISLAND OF NAVASSA. 



BY GEORGE W. TRYON, JR. 



The minute island of Navassa, a mere speck upon the 

 ocean, is over a hundred miles south of the eastern extremity 

 of Cuba, nearly as far east of Jamaica, laying between it and 

 Haiti — about fifty miles west of the latter. 



So extremely local is the distribution of the Terrestrial 

 Mollusks of the West India Islands, that such complete isola- 

 tion is the surest guarantee of its species being peculiar to it.* 



Until very recently, no species of shells were known to in- 

 habit Navassa ; but the introduction into the United States of 

 its rich guano, has made us better acquainted with its natural 

 productions. 



To Mr. Eugene Gaussoin, Mining Engineer, of Baltimore, 

 who recently visited the Island to report on its guano deposit, 

 for the Navassa Company, science is indebted for the collec- 

 tion of the following recent, as well as some fossil species of 

 shells ; and to my friends, Mr. Thomas Bland and Prof. F. Y. 

 Hayden, I am obliged for the opportunity of describing these 

 very interesting new species. 



1. Helix Gaussoini, Tryon. — t. 20, fig. 11. 



Description. — Globosely depressed, smooth, rather thick ; 

 spire depressed- conical, apex obtuse, suture moderately im- 

 pressed ; whorls 5|, convex, increasing slowly, not deflected 

 at the aperture ; aperture small, semilunar, labrum sharp, not 

 reflected, but much thickened at the base, and terminating in 

 the centre of the base of the shell, where it is considerably 

 impressed and dilated, covering the umbilicus. White, the 

 spire a faint flesh-color, (denuded of epidermis.) 



Dimemions. — Diam. 9, alt. 6 mill. 



Only one specimen of this species is before me ; it is some- 

 what related to the Cuban group to which H. melanocephalos, 

 &c, pertain. 



* See Bland's paper on the " Geographical Distribution of the Land Shells 

 which Inhabit the West Indies," published in the Annals of the New York 

 Lyceum of Natural History, Vol. VII. 



