32 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Mr. Smith) a single, shallow, but well-marked groove following the 

 suture about 6 mm. from it. This is also indicated on the edge of 

 the shell-lobe by slight notching or folding (Fig. 2). The inside 

 surface of the mantle zone resting against the umbilical margin was, 

 I noticed, of a red-brown colour, corresponding to the coloration of 

 the shell within the umbilicus. But it seems to me more likely 

 that this was a stain extracted by the alcohol from the shell after 

 death, rather than the remnant, in this part of the animal, of the 

 colouring matter which produces the band. 



The shell-muscle is strengthened by a peculiar, flattened, disc-like 

 expansion (s.m., Figs. 7-9), which I have not observed before in any 

 other species. Close to this, internally, are situated the attachments 

 of the retractor muscles of the buccal mass, amatorial organ, etc. 



Internal Anatomy. — The salivary glands are disposed in two thin, 

 flat masses, connected with each other and covering the stomach. 

 The buccal maw is short and flat on the basal side. The jaw (Fig. 10) 

 has a large central projection. 



The radula (Fig. 1 1 ) has the formulas — 



83 : 18 : 1 : 18 : 83 

 101 : 1 : 101 



The central tooth and 18 admedian teeth are straight- sided ; the next 

 34 lateral teeth — that is, up to the 52nd— arc aculeate ; the 31 uncini 

 are bicuspid. 



Genitalia (Fig. 6). — The amatorial organ, which is proportionately 

 of great length (75 mm.), tapers to the retractor muscle. The 

 spcrmatheca is long, broad at its base, gradually dwindling to 

 a well-defined connective muscle attached to the oviduct. The 

 male organ (Fig. 6a), which tapers from the generative aperture 

 backward, is bent on itself, the two portions being attached about 

 midway by muscular tissue (»?.). It then leads up to the short kalk 

 sac (/:.), and the vas-defcrens (v. d.) enters it at the side. Above the 

 bend a caecum is given off, which presents one single coil, and to 

 the rounded apex of this the retractor muscle is attached (Fig. 6a). 

 "VVe have here some interesting details illustrative of the variation met 

 with in these animals, and serving to distinguish this species from 

 other large forms. Compared with the type species of Hemiplecta, 

 the male organ is similar, save that in II. Humphreysiana there 

 is no ca3cum, whereas in this Perak species a cascum, approaching 

 in form that of Maerochlamys, is present. The spermatheca of 

 Hemiplecta Humphreysiana is rather short, and pear-shaped, not long, 

 and narrowing to an attachment muscle. There is some difference 

 in the relative position of the right shell-lobe in the two species : 

 in the Perak form it is given off at a lower point on the mantle 

 zone, and this is also the case in some other species. The radula 

 is of the same type in both, and if the admedians be added to the 

 curved aculeate laterals the number is identical, viz. 70 : 1 : 70, 

 the difference in the total number being made up in the outermost 

 bicuspid teeth. The jaw of the Perak snail has a much larger central 

 projection. These differences do not outweigh the similarity of the 



