408 



Mr. G. C. Robson on the 



2. Otoci/sts. — These are found in the usual position on the 



posterior sinface of the pedal ganglia. They contain 

 a single otolith. The auditory nerve is very difficult 

 to follow, and is apparently fused with the cerebro- 

 pedal connective. 



3. Ei/es. — These are situated at the base of the tentacles 



and on the outer side. They consist of inner and 

 outer corner, a well-developed lens, and retinal layer. 



(b) GiingUa and JServes. 



The cerebral ganglia are elongate and rather pointed ante- 

 riorly. They are placed with their long axes parallel to the 

 main axis o£ the pharynx. They are connected in the median 

 line by a small commissure. The pleural ganglia are closely 

 a])j)lied to the cerebral ganglia, but are not fused to the latter. 

 There are very short but distinct cerebro-pleural connectives 

 [('/'. discussion upon the latter in Paludestrina tilvce, llobsbn 



(12)]. 



Fi<?. 5. 



9<3C 



H. nosophora. Cerebro-pleural couiiective. 



?7j/=nglit pleural ganglion ; ?r^=right cerebral ganglion; 

 2)pc and c^jc = pleural-pedal and cerebro-pedal connectives. 



The cerebro-pedal and pleuro-pedal connectives are distinct, 

 though very closely applied to each other. The pedal 

 ganglia are rather round. They are closely approximated, 

 being joined by a small commissure. 



The supra-intestinal ganglion is joined to the right pleural 

 ganglion by a commissure slightly longer than that figured 

 by Breoenzer for Bythinella dunkeri (3). From this ganglion 

 are given off the osphradial nerve and a connective to the 

 abdominal ganglion. 



The subintestinal ganglion is ver}^ closely approximated to 

 the left pleural ganglion, but not fused to it. 



