PROiSTEOMENIA ACUMINATA. 219 



stichous type. The teeth (Plate 4, fig. 9) are comparatively small and delicate, 

 and as far as may be judged from cross sections number approximately twenty- 

 eight in each transverse row of which there appear to be about forty-five, though 

 this last estimate is difficult to prove definitely. The radular supports lack 

 the vesicular structures found in several other species of neomenians, and con- 

 sist entirely of a compact mass of muscle and connective-tissue fibres far too 

 intricate to define accurately from the study of sections alone. It may be said, 

 however, that close to the posterior end of the radula fibres pass to the overlying 

 pharynx or oesophagus, and others, much more powerful, extend from the 

 extreme posterior tip to the overlying radula sheath. In addition to these, 

 numbers of others extend from the radula sheath to the walls of the pharynx. 

 It thus appears that the radula, by reason of its intrinsic muscles, is capable 

 of considerable movement but probably, during the feeding process, the great- 

 est motion is produced by the protrusion and retraction of the pharynx which 

 carries the radula forward and backward. 



In Proneomenia hawaiiensis two well-defined subradular organs exist 

 innervated by fibres from ganglia, connectives, and commissure essentially the 

 same as in the Chitons for example. In the present specimen two patches of 

 modified cells, of the same character, exist and as they are in close proximity 

 to a pair of small ganglia it is reasonable to believe that here likewise we are 

 dealing with a definite sense organ. The component cells (Plate 4, fig. 10) 

 form knob-like elevations, surrounded by a shallow groove, on each side of the 

 forward border of the radula. Posteriorly they become continuous with the 

 ventral wall of the short, non-glandular ducts from the ventral salivary glands 

 so that the secretion from these organs pours over them in escaping into the 

 pharynx. 



In addition to these two modified areas the epithelium, continuous with 

 them across the mid line, is also of unusual height, being fully three times thicker 

 than that bounding the pharynx elsewhere (Plate 4, fig. 10). Its cells appear, 

 though not clearly, to contain small amounts of some faintly staining secretion, 

 but whether this is associated with a special sensory function has not been 

 determined since no definite nerve supply has been detected. 



Immediately behind the radula the pharynx unites with the stomach- 

 intestine \vithout any material change in the character of the epithelial lining 

 or the nature of its longitudinal folds. And furthermore the stomach-intestine 

 itself with its glandular lining and regular outpouchings does not differ from 

 the usual neomenian type, though certain features demand a brief description. 



