196 J. E. S. MOORE. 



descriptions given by Bouvier^ of the nervous systems of the 

 Scalarids and Solarium. It is unique in the enormous deve- 

 lopment of the pleuro-subintestinal cord, the whole of this 

 side of the nervous system being so disproportionate to the 

 otlier as to distinctly foreshadow the secondarily acquired 

 orthoneury of the Helicinidse. The almost complete fusion of 

 the cerebral ganglia in Ty phobia, and the reduced and 

 shortened-up pleuro-cerebral connectives, are conditions un- 

 doubtedly analogous to those obtaining in the Strombi, the 

 Pteroceras, the Cancellaridse, and other forms. The displace- 

 ment of the pleural ganglia and the almost complete disappear- 

 ance of the cerebro-pleural commissure on both sides, appear 

 to be characters peculiar to Ty phobia alone, while the position 

 of the otocysts in the head, and not in the foot, is most primi- 

 tive, but may have been accentuated by the forward displace- 

 ment of the pleural ganglia, and the consequent necessity for 

 the otocyst nerves to pass over these ganglia before they reach 

 the otocysts. On the other hand, the otocyst nerves are very 

 short, and even if the pleural ganglia were in their normal 

 position, the otocysts would still be very high up in the head. 

 The complete fusion between the pedal ganglia, and the pre- 

 sence of ganglionic cells in what remains of the pedal commis- 

 sure, lead to the same inferences as do the characters of the 

 cerebral ganglia. The great forward prolongation of the pedal 

 ganglia, and the ladder-like connections between the proximate 

 portions of the great anterior pedal nerves, are far more primi- 

 tive characters. These do, in fact, suggest that the approxima- 

 tion in the posterior portion of the nervous system to that 

 condition, of secondarily acquired orthoneury witnessed in the 

 Helicinidse, may not be altogether illusory after all. The 

 characters of the nervous system of Ty phobia show thus in 

 a manner which does not appear to be capable of serious dis- 

 putation, that this Gastropod has no relation to, nor indeed any 

 but the most remote phylogenetic connection with, the hitherto 

 recognised fresh-water forms. Nor has the nervous system any 

 of those characters which could be regarded as possibly pos- 



' Loc. cit. 



