MIUHRAXCHIATE GASTEROPODA. II 



convex; the anterior half between the projecting hinder edges of the mandibles is flattened and a little 

 hollowed; the posterior half is evenly convex, and from its middle arises the oesophagus, on either 

 side of which is seen a slight hollow with the apertures of the ducts of the salivary glands. 

 The sides of the bulbns pharyngens are evenly convex with a hollow behind the margins of the 

 mandibles (fig. 4). The lower side is anteriorly slightly convex with a hollow behind the mar- 

 gins of the mandibles, and behind this rises the strong radnla-sheath (fig. 4 e). As in the Pleuro- 

 phvllidiae and the Pleurolenridae, in Hero and Bornclla, and even in Scyllaea a thick muscular 

 plate (fig. 4,1) covering the greater part of the anterior surface of the mandibles, is found behind 

 and around the little labial disk; this plate showed a little below the middle of the fore side 

 a transverse, rather broad furrow; the thickness of the plate was about the region of the upper end 

 of the labial disk up to o, mni , decreasing upwards and downwards as well as towards the margins. 

 From the inner margin of the labial disk its coating continues as a thick dark blue or almost 

 black blue covering over the whole inside of (i. e. the opening of) the muscular plate, and attaches 

 near the free margin of the mandible '), in the middle at a distance of 6 mm from it, but upwards and 

 downwards approaching it, until the attachment in the uppermost and nethermost places almost 

 reaches quite to the edge. Above and below the same coating continues through the upper and 

 lower end of the slit between the margins of the mandibles to the backside of these, where it is 

 attached in quite a similar manner as on the foreside, the naked margin of the mandibles being, how- 

 ever, here only 4 mm broad in the middle. The covering is continued into the coating of the buccal 

 cavitv. When this muscular plate is removed the mandibles are naked ; the right one covered (pi. I, 

 fig. 6) with its marginal portion the margin of the left one (in the same manner as in the before ex- 

 amined form 1. The mandibles are strong and large, 29 ,nm long by a breadth of up to i7 mm ; resting 

 on the outer margin the mandible rose to a height of i8' nm ; in the marginal part the thickness rose 

 to almost 2 mm . Thev were of a fine horn-yellow colour, almost the whole of the inner half being 

 brown vellow. Their form (fig. 6) is oval, a little more rounded below than above (fig. 6a); the inner 

 edge is a little more projecting than the outer one, and tapers a little more towards the middle. The 

 mandibles are evenly bent from above downward ; they are thickest where the blue coating is attached, 

 decreasing in thickness towards the edge, especially towards the outer one, which is still somewhat 

 soft; thev are quite smooth on the surfaces, very finely concentrically and radially striated; the 

 masticatory edge was almost smooth. The mandibles join, and are immediately connected with each 

 other at the upper end, below they are a little apart (fig. 6). - The mandibles being removed the 

 anterior end of the muscular masses of the mandibles are uncovered, the colour of the inside of these 

 muscles (the cheeks) is dark blue, as is also that of the other parts of the buccal cavity, as well as 

 the tongue and the tectum raduke, to which the brown radula forms a rather strong contract. — The 

 tongue (pi. I, fig- 5) is very powerful, of the usual form, with a deep slit; in the buccal cavity it 

 projected j mm , and measured above from the base of the tectum radulse 15°"" in length; its height 

 (from above downward) was io, mm , and its breadth also ig mm ; the tectum radulae had a length of 7'5 mm , 

 anteriorlv it reached to the middle of the height of the tongue-slit. The radula itself was reddish 

 brown, somewhat glistening, its marginal part of a purple brown; its continuation into the sheath 



M Conip. 1. c. p. 113. pi. XIII. fig. 4. 



