286 SPIROSTEMMA. 



in Anoma the axis, while twisted, is not distinctly spiral, as it 

 is in Spirostemma. 



The Spirostemmas live on the ground in thickets, and from 

 their shape and color look like the pieces of broken twigs 

 among which they live, so that they are likely to escape notice 

 unless especially looked for. They occur in most parts of the 

 interior of Jamaica, and the genus is like Anoma in being 

 locally differentiated into a large number of species and races, 

 characterized by small but apparently rather constant differ- 

 ences, the main variation among individuals of any one place 

 being in size. The geographic ranges of part of the described 

 forms are unknown, owing to Professor Adams' unwilling- 

 ness to state the localities of his types. The characters of 

 part of the species have been but inadequately described. 

 These two circumstances, together with the great similarity 

 of the shells, render the determination of species difficult and 

 uncertain. 

 I. Axial well or false umbilicus visible in the aperture viewed- 



from below as a large hole. Group of 8. tenella, species 



no. 12 to 15. 

 II. False umbilicus not visible in the aperture, or only as a 



small hole. Group of S. dunkeri, species no. 1 to 11. 



Group of S. dunkeri. 



When some of these are better known they may prove to 

 belong to the group of S. tenella. 



Last whorl very shortly or not free, the peristome adherent 

 to preceding whorl above, or nearly so. 



No. 1. S. dunkeri. Length 6 to 7 times the diam. ; 15.3 x 2.7 

 to 20x29 mm., whorls 10y 2 -12y 2 ; brown; greatest 

 diam. at or below the middle. St. Catharine, St. 

 Elizabeth and Clarendon. 

 No. 2. 8. alia. 



No. 3. 8. bellevuensis. Length 4% times the diam. ; 13 x 3 

 mm., whorls 10; light brown; widest at the lower 

 third. Bellevue, St. Andrew. 

 Peristome free above, the last whorl built forward. 

 No. 1. 8. dunkeri. Last whorl only very shortly free. See 

 above. 



