368 PROCEEDINGS OF THE ACADEMY OF [L899. 



Affinities of Neobelisciis. 



Neobeliseus is a genus full of novel and interesting structures ; 

 and while future knowledge of those genera of Stenogyroid Acha- 

 tinicke of which the soft anatomy is yet unknown will doubtless 

 reduce the number of characteristics peculiar to the genus, it will 

 probably still remain somewhat isolated. The clumsy summit of 

 the shell, very different from the small bulbous nucleus of Stenogyra 

 obellsciis, Rumina decollata and other large forms, is one of the 

 obvious conchological stigmata. 



The dull silken lustre of the shell of the enormous uterine 

 young, produced by dense fine lamellose striae, and uncut by the 

 spirals which appear on the post-natal growth, is not paralleled in 

 Stenogyra, which is glossy at first. But it is in the reproductive 

 organs that the most striking features are seen. 



The penis is simple in structure, wanting the peculiar external 

 sheath so characteristic of Achatina ; but its retractor muscle arises 

 not from the diaphragm as in almost all Vasopulmonata, hnt from 

 the right tentacular and pedal band. It would not seem i-easonable 

 to question the homology of this penial retractor with the usual 

 one, but how so radical a change of base could have been effected 

 is problematic. We know of no other snail in which the tentacu- 

 lar retractor contributes a fascia to the genital system. The talon 

 (shown partially straightened out in fig. 5a, t. ) is large as in 

 Callionepion, but of a different shape. The attached portion of the 

 sperm duct is composed of a dense mass of radiating vermiform 

 tubules or cseca, a detail not drawn in the figure. The uterus in 

 virgin or functionally inactive individuals is shrunken, and lies in 

 numerous deep, regular longitudinal plaits. When carrying 

 young at almost full term it presents the appearance shown in fig. 



5, the young lying with the head directed anteriorly, the ventral 

 face toward the sperm duct. The head of the uterine young is re- 

 tracted ; and from the upper surf ace^of the foot, about the position 

 of the operculum in an operculate suail, there arises a flat membrane 

 which spreads over the ventral face of the young shell (PL XV, fig. 



6, ap.). From the hollow base of this placenta-like organ a duct 

 penetrates forward and upward through the tissues of the foot ; but 

 from the poor preservation of the infant tissues in our material we 

 could not ascertain what it communicates with. From what was 



