GIBBONS : ON OMALONYX UNGUIS AND O. FELINA. 1 01 



"the specific differences are not so easily impressed upon the 

 "shell as upon the soft parts." 



From the above it seems evident that the species found by 

 D'Orbigny in Bohna and collected by me in Bahia, is not the O. 

 z^;?o-///i' of Fe'russac; whether the Trinidad and Guadelupe mol- 

 luscs are one species is a point not yet, I beUeve, settled. 



The figure in Woodward would answer to either species 

 collected by me, except in regard to the spire, which is too 

 prominent for 0. felina, but exactly represents that of the Bahia 

 shell. 



Mr. Guppy, when separating the Trinidad Omalofiyx as a 

 distinct species, seems to have been guided more by the soft parts 

 than by the shell. It is in the shells however that the chief dis- 

 tinction lays — the difference in the animals depending on charac- 

 ters that are liable to considerable variation, e g.^ the shape and 

 degree of convexity of the body will be found to alter according 

 as the animal is more or less extended. 



According to Mr. Guppy's observations the mantle of 0, 

 felina is reflected over the shell, often completely covering it, but 

 occasionally retracted ^o as to expose the central portion. I have 

 repeatedly looked for this expansion of the mantle, both in the 

 Demerara mollusc and in the Bahia species, but although I kept 

 specimens alive for some time, I never saw more than a limited 

 portion of the margin of the shell enveloped. 



The eggs of Omalonyx, deposited at Bahia in the month of 

 September, bear a considerable resemblance to those of our larger 

 English slugs, having a semipellucid membranous capsule. 



November i^tJi^ i8j8. 



—^-oO*^^ 



