370 MR. J. H. VANSTONE ON" SOME POINTS IN" THE 



proportion to the size of the animal's body, for in a specimen 

 whose shell was 12 centimetres long and 8 centimetres broad at 

 its widest part, the stomach only measured about 9 by 2*5 milli- 

 metres. In none of the specimens examined did the diameter 

 exceed 3 millimetres. The calibre of this organ is but slightly 

 in excess of that of the oesophagus and intestine, and in this it 

 differs from M. tuba, in which the stomach is more expanded and 

 sac-like. 



The chief point of interest, however, is not seen until the 

 stomach is opened, and if present in M. tuba it was overlooked by 

 Souleyet. Within the stomach of M. melongena, on the upper 

 and lower walls, there is a longitudinal series of hard cuticular 

 plates and knobs lineally disposed on a median ridge (jp-g- p-g.", 

 tigs. 3, 4). At the curvature of the stomach the rows take 

 their origin in an irregular group of somewhat larger knobs 

 and they are continued down to within a short distance of the 

 opening of the bile-duct (b.d., fig. 3). The above-mentioned 

 oesophageal ridges bear, when near the stomach, long claw-like 

 plates fixed only at their anterior ends. Both oesophageal 

 {p.ce., fig. 4) and gastric plates are freely movable on their bases 

 of attachment. 



In the stomach of two species of Crepidula *, Haller has lately 

 described swellings bearing a thickened projecting cuticle, and 

 these he believes effect a retardation of the flow of food-material. 

 These structures, from their general characters and position, 

 must be the same as those met with in Melongena, where they are 

 more strongly developed. The function of retardation in Melon- 

 gena would, I think, be sufficiently ensured by the small calibre 

 of the intestine, assuming that that function be necessary. It 

 seems more probable that these tough, apparently chitinous, 

 plates effect a trituration of the food, as is undoubtedly the case 

 in Pteroceras, where similar cuticular processes exist f. The 

 homology of the parts, as seen in Pteroceras, with the " sagitta 

 tricuspidis " of Lamellibranchs has been pointed out by Barrois % 



* B. Haller, " Die Morphologie der Prosobranchier, iii.," Morph. Jalir. xviii. 

 p. 602. 



t T. H. Huxley, "Morphology of the Cephalous Mollusca," Phil. Trans, 

 1853, pp. 29, 66. 



I T. Barrois, " Le stylet cristallin dea Lamellibranches," Reyue Biol, du 

 Kord, 1890, No. 8, p. 310. 



