54 HELIClD.i:. 



have of the lungs of both groups ; and that we do not yet know 

 enough of the anatomy of Plectopylis, Stegodera, or TrmimatopJiom, 

 to demonstrate any relationship between them and CoriJIa, though 

 it is natural to suppose that these genera stand together. The 

 genus, so far as we now know, stands by itself, lie says, and for 

 it alone a subfamily Corillinse must be erected, which for the 

 present might be placed next to the Cama^ninge. 



Lt.-Col. God win- Austen, on the other hand, considers that the 

 generative organs in Gorilla are remarkably similar to those of 

 Fleciojpylis, while another striking character common to both 

 genera is found in the liver. 



Albers in 1850 established the genus Atopa for the reception of 

 three species previously classed in Heliv, i. e. acJiaiina, Gray, 

 refur/a, Gould, and rivolii, Desh. The name being preoccupied in 

 Coleoptera (Fabricius, in Paykull, Faun. Suec. ii, 1799, p, 116). 

 H. and A. Adams in 1855 proposed Gorilla in lieu, adding a fourth 

 species, erronea, Alb. No type was indicated, but the first of the 

 species enumerated being acJiatina, the name Gorilla would, under 

 a strict application of the law of prioi'ity, have to be assigned to 

 Helicc achatina and its allies, while Plectopylis would become a 

 synonym. No useful purpose, however, would be served by such 

 a process ; on the contrary, much confusion would arise, and it 

 therefore appears advisable to accept the status of these two 

 genera as defined by Benson and Pilsbry. 



The genus Gorilla is especially remarkable from the fact that 



the immature shells are provided with barriers which invariably 



differ from those found in full-grown ones. The parietal folds 



are not formed until the sliell approaches completion, while the 



palatal lamellae of immature shells are always much larger, being 



almost triangular, overlapping, and reaching nearly to the ])arietal 



wall. From what we know of the retention of ancestral characters 



in young individuals, as explained by Darwin (' Origin of Species,' 



sixth edition, p. 388), it may, I think, safely be assumed that the 



immature form of barriers found in the young shells represents 



the form of lamelljB which were possessed by the prog(mitors 



from which the existing armed members of the genus have sprung. 



Consequently, those species A\hich have to some extent retained 



such characters in the adult stage (i. e. Gorilla anax and 



G. heddomece) are the older forms ; while those species Avhich 



have diverged most in the adult state (?". e. the group of C erronea) 



are of more recent origin. A singular fact in this connection is 



that whereas in the adult state G. adamsi possesses no armature, 



immature shells are provided \\\t\\ five palatal lamella?, the same 



as obtains in the other members of the genus. When publishing 



my observations on the armature of the various species of Gorilla 



in 1896 I was ignorant of this fact and I am not aware that this 



has e^er been pointed out. Among a number of shells in various 



stages of growth, sent to me by the late O. Collett, were several 



young specimens of G. adamsi, and upon opening these I 



discovered that they were furnished with palatal lamella? similar 



