18 PROCEEDINGS OF THE ACADEMY OF [Jan., 



The change of sculpture which accompanies the reduction in 

 size is to be differently explained in the case of each species. In 

 the one case, that of L. granulosa, it has been shown to be directly 

 connected with the reduction in size, which in turn is brought about 

 by the loss of a whorl. The sculpture in this case is that of the 

 young shell up to the beginning of the sixth whorl (up to 5.3 whorls 

 generally), and is a necessary accompaniment of the loss of a whorl. 

 In the case of normal forms in which this sculpture exists, as in the 

 occasional specimens from Somerset or the Swift Collection speci- 

 men of L. granulosa, this sculpture seems to have persisted up 

 to the end of the sixth whorl; and, as pointed out, it may be an 

 ancestral character which is becoming obsolescent. But it has been 

 rejuvenated in these dwarfed forms by the process known as rever- 

 sion. 



The case of the change of sculpture in the dwarfed forms of 

 L. aureola is different. Here we are not dealing with a character 

 which exists in the young stages and is simply disclosed by the 

 leaving off of a whorl, as in the last case, but with a new character 

 of which no trace is to be found in the young of the normal species. 

 It may be an adaptation in response to the change of environment 

 or it may be due to the effect of hybridity. It is here that the evi- 

 dence is incomplete. 



It is not known whether the other form that would likely hybridize 

 with L. aureola occurs (or has occurred) at Montego Bay. I mean 

 the species L. granulosa. In a large collection made at Montego 

 Bay in 1910 I did not encounter this species, nor is it found in 

 Henderson's list® as being found at this point. It might be found 

 in some of the deposits of semi-fossil shells that occur near Montego 

 Bay, but while I examined these, I did not find any specimens of 

 L. granulosa. If it existed at Orange Hill and at Rose Mount pre- 

 vious to the clearing of the land it would probably die out, as this 

 species requires more cover than is to be found in the logwood-planted 

 pastures where the Montego Bay race of L. aureola is now living. 

 And during its extinction it might very conceivably have mixed 

 with the L. aureola, which thrives well in grass lands elsewhere in 

 the island. The hybrid thus produced would be likely to have a 

 tuberculated .periphery. And the hybrid living with a normally 

 sculptured, pure race of L. aureola would tend through hybridity 

 to change back to the normal sculpture of this latter species. 



« J. B. Henderson, Nautilus, VIII, 1894, pp. 1, 19, 31. 



