628 NOTES ON PROSOBRANCHIATA, 



identify any of them, the nervous system not being decipherable 

 in my serial sections. The two inner ones {c.h.con.) are believed 

 to be the cerebro-buccal connectives. It is also believed that the 

 labial circle described for Nassojysis by Moore (13) exists in this 

 genus also, but this is entirely uncertain. A nerve rising from 

 the posterior and inferior face of the right cerebral ganglion 

 (n.gen.) often comes away with the ganglion. After running a 

 rather short course it splits up into several fine branches. It has 

 not been seen in situ, but possibly innervates the genitalia on 

 the body wall. Inferiorly both cerebral ganglia are connected 

 by their respective commissures (c.pd.con.) to the pedal ganglia. 

 Posteriorly the cerebro-pleural commissures (c. pi. con.) are given 

 oflf, and connect the cerebral and pleural ganglia. The left 

 cerebro-pleural connective is longer than the right. The pleural 

 ganglia (pl.g.) are also connected directly with the pedal ganglia, 

 the pleuro-pedal connectives (pl.pd.con.) being stouter than the 

 cerebro-pedal connectives. 



The left pleural ganglion is connected directly wdth the sub- 

 intestinal ganglion {sh.iiit.g.). Two other nerves arise from the 

 left pleural ganglion; one of these {dialxon.) passes just under 

 the floor of the body cavity in the direction of the left visceral 

 nerve {n.v.'), with which, although it has not been traced so far, 

 it possibly connects, causing a condition of dialoneury on the left 

 side. The third nerve rising from this ganglion is probably the 

 columellar nerve (n.coL). The right pleural ganglion, besides 

 being connected to its fellow pedal and cerebral ganglia, is also 

 connected by the supra-intestinal commissure (sp. int. con.) to the 

 ganglion of that name (sp.int.g.). The supra-intestinal commissure 

 is longer than is the subintestinal commissure. There are no 

 nerves taking rise from the right pleural ganglion, so that there 

 is no connection between that and the subintestinal ganglion. 

 Both supra- and subintestinal ganglia give rise to the respective 

 pallial (n.pal.) and visceral nerves (n.v.). The pedal ganglia 

 (pcl.g.), as in Littorina, are of a large size, and give rise inferiorly 

 to numerous nerves, none of which have I been able to identify. 

 A peculiar ganglionic knot (p.g.k.), partly divided from the 



