22 



dorsarside of the odoutopliore under the commencement 

 of tlie gullet (fig. 12). This cavity narrows behind into 

 the radular sac. 



(h) Within the dorsal and ventral outer lips an 

 inner lip is present on either side as an upwardly grooving 

 fold (fig. 6). Boutan refers to this pair of lips as " unc 

 levre en forme de fer a cJieird.'"' These two lips can be 

 approximated so as to close the mouth almost entirely. 

 A median papilla, or "licker," belonging to the 

 odontoi)hore, projects between the lips so as to com- 

 pletely All the chink i)etween them when the mouth 

 is closed. 



(c) The dorsal palatal plate is a chitinous sub-epithelial 

 thickening forming an arch over the region of the inner 

 lips. It imparts firmness to the lip and alsf) serves to 

 lift the tissues connected with it out of reach of the 

 rasping radula. It is prolonged into two pairs of 

 expansions, one pair dorso-lateral and one pair ventro- 

 lateral (fig. 11). This plate is most probably a pair of 

 jaws united by a median dorsal piece. 



(d) The front end of the odontophore or rasping organ 

 23rojects into the palatal section of the buccal cavity from 

 its postero- ventral wall, and the front end of the radula, 

 a horny tooth-studded ribbon, occupies a narrow median 

 strip on this jjrojection (fig. 12), extending backwards on 

 the posterior part of the odontophore cushion, which is 

 placed beneath the fioor of the post-palatal section of the 

 buccal cavity (a above) underlying the gullet. The 

 epithelium covering the tip of the odontojjhore, anterior 

 to the radula, has grown out into a transversely ribbed 

 projection, which is the papilla, or " licker." 



(c) The sub-lingual pouch is a recess below the front 

 end of the odontophore (fig. (i). It is found in Chiton 

 and manv other forms. In VutcHa it is lined bv 



