INCISUEA (sCISSUEELLA) LYTTELTONENSIS. 23 



band of ciliated cells which diverges tovvai'ds the left, and 

 eventually passes completely over to the left side and passes 

 into the nai-row posterior part of the oesophagus. Ventrally, 

 to the right side of the narrow oesophageal tube, the floor of 

 the spacious anterior oesophageal cavity is produced into a 

 capacious pouch or "jabot/' which runs back for some 

 distance alongside of the narrow oesophageal tube (fig. 11, j), 

 and eventually ends blindly. Tlie deviation of the oesophagus 

 to the left and the preponderant size of the right oesophageal 

 pouch have been noted b}^ Boutan in Fissurella, and it is 

 indeed a cotntnon feature in the Rhipidoglossa, indicative, as 

 Amandrut has pointed out, of the larval torsion which brings 

 about the asymmetry of the adult Grastropod. 



The nervous system. — Fig. 5 is a diagram of the prin- 

 cipal ganglia and nerve-trunks, as reconstructed from sections. 

 Pelseneer's description of this system in Scissurella costata 

 and Incisura ly ttel tonesi s is as follows : " Dans les deux 

 especes, les cordons pedieux sout dans la masse musculaire 

 du pied, et s'etendent jusqu'a la partie posterieure. A leur 

 extremite tout a fait anterieure se trouvent des ganglions 

 pleui-aux bien distincts. La commissure viscerale na'it de ces 

 derniers ; elle est croisee et porte un ganglion supra-intes- 

 tinal presque accolle au ganglion branchial ou osphradial 

 gauche, comme dans Ti^ochus. Tout ce systeme nerveux 

 ressemble done beaucoup plus a celui de Trochus qu'aux 

 parties correspondantes conuues de Pleu rot om aria, telles 

 que les out decrites Bouvier et Fischer." Since this was wi'itten 

 we have had the more complete account of the anatomy of 

 Pleurotomaria by M. F. Woodward, and the difference between 

 the nervous system of this genus and that of the Scissurellid^e 

 is even more apparent than before. 



As may be seen from the dingiam, the nervous system of 

 Incisura is at once typically Rhipidoglossate and specialised. 

 As the nervous systems of various Rhipidoglossa have been 

 described in great detail by sundry authors, it will only be 

 necessary here to mention the more important and peculiar 

 features. 



