GUPPY : MOLLUSCA OF TRINIDAD. 215 



A minute unibilicate heliciform shell, with 5 — 6 whorls. 

 Height f mill., diameter i|- mill. 



The difficulty here again arises with reference to these two 

 species as to which is their true generic position. 



In my original description of Zonites iimhratiUs there was 



an error, as pointed out in a note to page 207 of ' Amer. Jour. 



Conch.,' 1870. The umbilicus is deeper but not wider than it 



is in Z. hnplicafis. The difference in the form of these shells is 



made evident by the figures cited above. These differences are 



similar to those between H. ammoniforniis Orb. and H. bourno- 



bcena Orb. (Amer. Merid.), which are possibly allied to our 



species. 



10. Guppya livida Guilding. 



Guppya vacans Crosse, I.e., p. 38, No. 5. 



This varies so much in shape at different stages of growth 

 that young and adult examples might easily be taken for 

 different species. The texture is transparent shining horny 

 brown, with microscopic revolving and cross lines. The surface 

 sharacters of the shell are like those of Comihis chersina Say, as 

 figured by Morse in the Journal of the Boston Society of 

 Natural History (1864). The young shell is subperforate and 

 its whorls are carinate. As it grows these characters become 

 modified, and the contour becomes more rounded. 



It would be difficult to say what species should be assigned 

 to the genus, but Gicppya selenkai of Mexico is one, and G. 

 gnndlachiVL another. (See Tate, 'Amer. Journ. Conch.' 1868, 



P- 154- 



II. Macrocyclis alicea Guppy. 



Hyalina alicea Crosse, I.e., p. 39, No. 9. 



A depressed planorbiform shell of about 5 — 6 whorls, 



rather evenly convex above and openly unibilicate beneath. 



Diameter 8 mill, height 2| mill. In shape it approaches If. 



concolor P'er., but its color and texture are more like those of 



Macrocyclis concava. It is, however, much smaller. This 



species, found only in the northern mountains of Trinidad, 



