228 GUPPY : MOLLUSCA OF TRINIDAD. 



expanded or double concentrically-striate lip. Height 13 mill, 

 diameter 8 mill. 



Bland (in 'Amer. Journ. Conch.,' 1868, p. 179) remarks 

 the resemblance of this shell to Chondropoma cordovanum 

 Pfeiff., but I think there can be no doubt of its very close 

 affinity to Clshila tavisiaiia Pfeiff of the neighbouring mainland. 



I have observed the existence of two forms in this as in 

 other species of mollusca. These two forms are males and 

 females. The males are constantly smaller than the females. 

 I have noticed this in Bulinuis ob!o?igus, which I believe to be 

 always functionally unisexual whether or not it is so anatomi- 

 cally ; and it is well-known that in certain species (e.g. 

 CyclopJiorus pearsoni Bens.) there are a large and a small form. 

 These I take to be females and males respectively. 



52. Helicina nemoralis Guppy. 



Crosse, I.e., p. 58, No. 55, pi. ii,, f. 8. 



A smooth pinkish or yellowish species belonging to the 

 same group as H. coluinbiana Phil., Zephyrina Duclob, and 

 jamaicensis Sow. 



53. Helicina barbata Guppy. 



Crosse, I.e., p. 58, No. 56, pi. 2, f. 9. 



A more obscure and much more common shell than the 

 last. It is stated to be near to or identical with H. dysoni 

 Pfeiff, but I have not been able to demonstrate this identity. 



54. Helicina lamellosa Guppy. 

 'Ann. and Mag. Nat. Hist.,' 3 sen, vol. xix., p. 260, pi. x., f. 4. 

 Crosse, 'Journ. de Conch.,' 1890, p. 59, pi. ii., f. 10. 



A spirally lirate species belonging to the same group as 

 H. semistriata Sow., H. lirata Pfeiff., and H. H/ieata Adams. 

 I have designated this group by the name of Peretina. 



J.C, vii., Oct. 1893. 



