Farnie. — The Structure of Ampliibola ci'enata Martyn. 75 



line. If the radula is mounted whole, only two kinds of teeth are visible, 

 as it is very difficult to spread it out flat, but if separated with needles three 

 distinct kinds can be distinguished (fig. 4) — (1) central, (2) lateral, 

 (3) marginal. 



The central tooth {tc) has a broad base, bearing a median cusp which 

 is almost scpiare in outline. On either side of this are a number of smaller 

 cusps, six or seven, but the number differs with each central tooth and 

 often on the two sides. The cusps next to the median on either side are 

 smaller than those more remote ; but all taper to a sharp point. On either 

 side of the central tooth, and placed slightly above its upper margin, is a 

 small elongated lateral tooth {tl) which is somewhat blunt at the tip. Next 

 to this is another lateral tooth, of larger size, wdiich bears two cusps. The 

 division into cusps is not the same in every tooth. Some have a large outer 

 cusp and a very small, narrow inner one ; in others the cusps are of equal 

 length and breadth. But this difference is due probably to some being 

 more worn away than others. The remaining teeth on each side of the 

 laterals are the marginals {tyn). They are all curved, simple, conical teeth, 

 the tips of which are somewhat rounded. 



Hutton (1879) describes only two kinds of teeth in the radula of Amphi- 

 hola — median and lateral. He also says the apices of the teeth point for- 

 ward. He gives a very rough sketch of the radula, but the shape is not 

 correct. In his second paper (1882) he redescribes the teeth. He notes 

 that the median tooth hks five or six cusps on either side, not two or 

 three as he formerly thought ; that there is a single lateral tooth, which 

 is often divided into two and varies in shape ; and that the rest of the 

 teeth are aculeate, and increase in length towards the margin. 



The form and great size of the median tooth in Amphihola seems 

 unusual among pulmonates, for, judging from figures of radulas of other 

 pulmonates (Bronn's Thierreich, pi. xcv) — e.g., SipJionaria, Limnaeft, 

 Planorbis, Auricula — the median tooth is much smaller and simpler than 

 those on either side. 



Perrier (1897) says that the form of the lingual teeth is related to diet : 

 that they are obtuse and generally numerous in herbivorous molluscs, but 

 have the form of a hook and are less numerous in carnivorous genera. 

 The teeth in Amphibola, therefore, agree with those of other herbivorous 

 molluscs. 



A pair of salivary glands open into the buccal cavity (fig. 3, sg) near 

 the commencement of the oesophagus. Each gland is a long, linear, yellow, 

 sacculated structure, which passes through the nerve-collar and runs for 

 a short distance backward beside the oeso])hagus. Posteriorly they ta])er, 

 and are attached together and to the wall of the oesophagus. 



The oesophagus extends backwards for about two-thirds the length of 

 the body. The posterior portion lies beneath the intestinal coil, and is 

 visible by transparency on the ventral surface of the uninjured animal. 

 As far as the intestinal coil the oesophagus is a narrow tube, but it then 

 dilates a little, the dilatation being marked off from the portion in front 

 and behind it bv constrictions. This specialized portion of the oesophagus 

 is the crop (c). Behind the crop the oesophagus becomes broader, and on 

 a level with the posterior end of the intestinal coil it bears a finger-shaped 

 diverticulum on the right side [cliv). Behind this diverticulum the oeso- 

 phagus becomes broader, and opens into the stomach {st), which is U-shaped, 

 the right limb being much smaller and narrower than the left, which 

 extends forwards towards the heart. An outgrowth of the left limb of the 



