20 GILBERT C. BOUKNE. 



very closely resembles that of Subemarginula picta, the 

 shape and relative size of the outer medio-lateral tooth Vjeing 

 almost identical, as also the characters of the centrals and 

 uncini. The large and specialised outer lateral tooth, though 

 it differs widely in detail in different species, is chaiacteristic 

 of the Fissurellidas, A close resemblance also exists between 

 the radula of Incisura and that of Emarginula pileolus, 

 and a less clearly marked resemblance can be seen in the 

 radulae of various species of Fissurella. Ou the other hand, 

 no comparison with the radula of Pleurotomaria is possible. 

 A general view of the alimentary tract, as determined by 

 reconstruction from sections, is given in fig. 3, which so far 

 explains itself that little description is necessary. The oeso- 

 phagus is enormously dilated in the anterior part of its course, 

 forming in addition to the wide lateral diverticula or ossopha- 

 geal pouches (figs. 9 and 10, ce. f.) a spacious ventral pocket 

 or '' jabot." These are all lined by a soft-looking glandular 

 epithelium. Behind the level of the pedal ganglia the 

 posterior section of the oesophagus leaves the jabot as a 

 narrow tube with thick, longitudinally ridged walls formed by 

 a long ciliated columnar epithelium. It runs back below the 

 stomach and opens into the latter near its posterior end. 

 Near the oesophageal opening numerous liver caeca open into 

 the posterior end of the stomach. There is no spiral ctecum 

 connected with the entry of the liver-ducts as in Pleuroto- 

 maria, Haliotis, and Trochus, but there is a deep ciliated 

 ventral groove, the lips of which are bordered by specially 

 long ciliated columnar cells, extending along the floor of the 

 stomach from the oesophageal opening to the pylorus. A 

 precisely similar groove occurs in the stomach of Fissurella, 

 and has been well described and figured by Boutan (2). 



Randies has shown that in Trochus a ctecal groove, bounded 

 by two conspicuous folds, extends into the spiral caecum from 

 the CBSophageal opening, and that the larger of the two bile- 

 ducts opens into this groove. Though the spiral caecum is 

 absent there can be little doubt that the ventral groove of the 

 Fissurellidae and Incisura corresponds in function to the caecal 



