INCISUEA (sCISSUEELLA) LYTTELTONENSIS. 25 



ganglia isan indication of specialisation and apeculiarfeature in 

 lucisura. For the rest the characters of the cerebral ganglia, 

 the size of their labial lobes, and the relations of the buccal 

 ganglia are very similar in Turbo, Fissurella, and Incisura. 



The cerebro-pleural connective, as is commonly the case, is 

 larger than the cerebro-pedal ; both are true nerves, devoid of 

 any sheath or local accumulations of ganglion cells. The 

 pleural ganglia are distinct and that of the right side is 

 relatively large, but both are fused to the dorsal surfaces of 

 the pedal ganglia. The visceral commissure is typically 

 streptoneurous, and for the same reason that the osphradial 

 ganglia are situated far forward, the whole commissure is con- 

 tracted antero-postei'iorly as in Patella ; on the other hand, it 

 is considerably extended right and left. The sub-intestinal 

 ganglion is distinct, but elongated and rather ill-defined ; as 

 Pelseneer remarks it is connected by a very short nerve with 

 the large left osphradial ganglion. The left symmetrical 

 pallial nerve passes straight out from the left pleural ganglion 

 almost immediately below the supra-intestinal ganglion, 

 and traverses the posterior fibres of the left columellar 

 muscle, turning neai'ly vertically downwards to enter the 

 thickened border of the mantle. Before turning downwards 

 it gives off a very fine branch, which makes connection with 

 the short nerve uniting the supra-intestinal with the osphradial 

 ganglion, thus establishing a left-hand dialyneury very 

 similar to that of Trochus. 



The subintestinal nerve is very stout, and crosses over the 

 dorsal surface of the hinder part of the pedal ganglia almost 

 at right angles to the long axis of the body. The sub-intes- 

 tinal ganglion is fairly large and distinctly indicated by an 

 accumulation of nerve-ganglion cells. It is triangular in 

 shape, and from its right-hand lower corner the visceral nerve, 

 and from its right-hand upper corner the osphradial nerve is 

 given off. The latter is a very slender nerve, which passes 

 into the substance of the columellar muscle, and turns verti- 

 cally downward and then forward along the dependent edge 

 of the mantle, running in this part of its course at the base 



