54 



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

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

 to demonstrate any relationship between them and Gorilla, though 

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

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

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

 present might be placed next to the Camaenmae. 



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

 generative organs in Gorilla are remarkably similar to those of 

 Plectopylis, 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 Helix, i. e. achatina, Gray, 

 refuga, 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 achatina, the name Gorilla would, under 

 a strict application of the law of priority, have to be assigned to 

 Helix 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 shell approaches completion, while the 

 palatal lamellae of immature shells are always much larger, being 

 almost triangular, overlapping, and reaching nearly to the parietal 

 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 lamellae which were possessed by the progenitors 

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

 Consequently, those species which have to some extent retained 

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

 G. beddomece) are the older forms ; while those species which 

 have diverged most in the adult state (i. e. the group of G. 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 with five palatal lamellae, 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 lamellae similar 



