768 PROP. G. C. BOURNE ON THE 



diverticulum is composed of very long attenuated epithelial cells, 

 among which are long club-shaped glandular cells. This glandular 

 stiip may be traced upward and forward to the thickened lip of 

 the oesophageal opening, where it forms a prominent ridge 

 which passes above into the anterior pair of salivary glands, to 

 be described shortly. 



As is shown in PL XXX. fig. 2 and in the section drawn in 

 fig. 4, the radular sac opens into the pharynx by a widely gaping 

 aperture situated in the trough- shaped depression between the 

 anterior ends of the anterior odontophoral cartilages. Posteriorly 

 the radular sac passes between the posterior odontophoral cartilages 

 and runs at first to the right of and below the cesopha,gus, but 

 soon mounts upwards and to the left, the two organs, oesophagus 

 and radular sac, being twisted round one another as shown in 

 fig. 2. The radular sac is short in Alcadia palUata and is of no 

 great length in any of the species that I have studied. The greater 

 or less length of the radular sac appears to be an individual rather 

 than a specific character. The charactei'S of the radular teeth will 

 be dealt with in a separate section. 



The odontophoral cartilages were described in some detail by 

 Isenkrahe for Helicina titanica, and I have but little to add to his 

 account. A ventral view of these structures in Alcadia jmlliata 

 is given in PI. XXXI. fig. 5, and a sketch of a dorsal view of the 

 same structures in Eutrochatella pidchella in fig. 6 : both figures are 

 drawn to the same scale. As may be seen from the specimens 

 figured, the odontophoral cartilages exhibit specific diffei-ences in 

 relative size and proportion, but these differences are of too slight 

 and elusive a chaiacter to be expressed in a description, and scarcely 

 important enough to make it worth while to give a separate figure 

 for each species examined. The essential structure is the same 

 in all. There are two pairs of cartilages, an anterior and a 

 posterior. Each member of the anterior pair is a plate having 

 the form of a more or less elongated isosceles triangle ; the 

 margins of the plate are thickened and rounded, the central 

 portion remains thin. The plate is bent in such a way that its 

 lower margin is bent inward posteriorly and its upper margin 

 outward. The posterior margin or base of the triangle, forming 

 the articular surface for the posterior cartilage, runs obliquely 

 from above downwards and inwards. The lower mai'gins of the 

 two cartilages are connected by a tough fibrous band, and their 

 thickened edges serve for the attachment of the intrinsic and 

 extrinsic odontophoral muscles. The posterior cartilages are 

 short conical masses ; their apices directed backwards ; their 

 ventral surfaces convex and their dorsal surfaces more or less 

 concave. Their bi-oad anterior ends are shaped to correspond with 

 the articular surfaces of the anterior cartilages, and the two are 

 firmly held together by musculai- fibres, whose arrangement is 

 indicated in fig. 5. It follows from the above description that 

 the odontophoral cartilages form the sloping sides of a V-shaped 

 trough, the concavity of which looks upwards and supports the 



