74 



flat, horny, mandibular plate, of the shape shown by text figure 2. 

 Each plate is composed of fine rodlets, which are inclined to 

 the surface in such a way that they overlap each other, leaving 

 only the heavy, bluntly-pointed ends projecting and pointing 

 toward the concave anterior border. 



The pharynx (buccal mass) is large and muscular, the in- 

 trinsic circular and longitudinal muscles, as well as its retractors 

 and protractors, being well developed and defined (fig. 15, 

 Plate III). The tongue is large and firm, is quite regularly 

 ovoid in shape, and occupies most of the floor of the pharynx 

 (fig. 13, Plate III). The anterior surface presents a median 



point, from which a frenum-like ridge 



extends along the floor of the pharynx 

 to the mouth; the posterior end of the 

 tongue overhangs the base. The radula 

 is light brown, broad, depressed along 

 the median line, acutely pointed at the 

 anterior end, and rounded posteriorly. 

 The widest part of the radula lies upon 

 the posterior face of the tongue. Ab- 

 sorption of the lateral teeth commences 

 at the posterior limit of the anterior face 

 of the tongue and proceeds inward from 

 this point, resulting in the pointed an- 

 terior end of the radula already referred 

 to. The radular sheath lies under the 

 posterior end of the tongue, and is broad 

 and shallow. A transverse arcuated 

 fold of the floor of the pharynx lies be- 

 hind and parallel to the base of the 

 tongue. 



On each side a broad fold of mucous 

 membrane projects from the lateral wall 

 of the pharynx above the posterior portion of the tongue. In 

 the unopened pharynx the free medial edges are applied closely 

 to each other, completely separating the anterior, muscular- 

 walled part of the pharyngeal cavity which contains the tongue, 

 from a thin-walled posterior portion which opens directly into 

 the oesophagus. The inner (ventral) surfaces of the folds are 

 fairly smooth, the outer surfaces corrugated. The apertures 

 of the salivary ducts are on the inner surfaces of these folds, 

 near their anterior extremities. The mucous membrane of the 

 pharynx is pigmented in black spots and lines. 



Fig. 2.— Outline of a man- 

 dibular plate of Aclesia 

 f r e e r i sp. nov. The 

 figure within the out- 

 line represents four of 

 the rods of which the 

 plate is composed. The 

 concave border of the 

 plate is anterior. Ac- 

 tual dimensions, 5 milli- 

 meters high, 3 milli- 

 meters wide at bottom, 

 1 millimeter wide at 

 top. 



