100 BRACHYPODELLA, JAMAICAN. 



typical form, except in being smaller, with fewer and slightly 

 more convex whorls, occur at Creighton Hall (pi. 2, f. 16), 

 measuring from length 25.6, diam. 3.9 mm., whorls l5 l / 2 , to 

 length 19, diam. 3.2 mm., whorls 



45. B. DIMINUTA ' Ad.' Pilsbry, n. sp. PI. 2, figs. 17, 18, 19. 



Shell pillar-shaped, slightly tapering and truncate above; 

 thin, whitish. Densely sculptured with extremely narrow, 

 thread-like, oblique, opaque-white strias, standing on a trans- 

 lucent-gray ground. Whorls convex, the latter part of the 

 last projecting free. The neck is squarish, pinched into a 

 strong basal keel, the peripheral keel wider; it is angular 

 above, and the columellar side is strongly convex. Aperture 

 rounded, angular outwardly and below, channelled within. 

 Lip thin, expanded and reflexed. Axis slender and simple 

 above, thicker in the lower half, where it bears an upper and 

 lower series of oblique nodes, terminating in hooks, opposite 

 to and directed towards each other. 



Length 19, diam. 2.7 mm., whorls 15. 



Length 17, diam. 2.75 mm., whorls 15. 



Jamaica: Good Hope, near Flamstead, in the eastern part 

 of St. Andrew parish (Jarvis). Types no. 84971, A. N. S. P. 



Cylindrella agnesiana var. diminuta C. B. AD., Contrib. to 

 Conch., no. 9, p. 160 (April, 1851), in Ann. N. Y. Lye. of Nat. 

 Hist., v, p. 84. 



Smaller than ordinary B. agnesiana, though the smallest 

 shells of that species are equally short, but of greater diam- 

 eter; chiefly distinguished by the extraordinary modification 

 of the axis, on which the two spiral cords of the less modified 

 species of the group are interrupted and transformed into 

 nodes ending in hooks. The structure is exceedingly like that 

 of Idiostemma (cf. U. uncata, Vol. XV, p. 166, pi. 44, f. 33). 

 This is the most extraordinary case of convergent evolution I 

 have ever seen. 



C. B. Adams did not properly define this species. His 

 account follows: " We are indebted to Dr. A. Barrett for this 

 remarkably small variety with the following dimensions : 

 length after truncation .67, breadth .22 inch. In the speci- 



