6 SIR C. ELIOT. 



and the posterior lobe is rather deeply divided. An operculum is often present in 

 specimens of both small and moderate size, certainly in several which have a 

 diameter of at least 3 mm., but is absent in the largest and is probably caducous in 

 adult life. It is much as figured by Pelseneer (' Belgica,' figs. 70, 7l) and has a 

 short sinistral spire of two whorls (fig. 2). The balancer or long narrow lobe on the 

 right side of the mantle is well developed. 



The jaws mentioned by some writers could not be found by ordinary dissection, 

 but in transverse sections there were seen in the part of the buccal tube lying in 

 front of the radula, dark pigmented folds covered by a very thin layer of a lighter 

 colour and apparently chitinous. In the floor of the cavity are two ciliated grooves 



(fig- 3)- _ 



In individuals having a diameter of 3 mm. or more the radula consists of 



8-11 rows containing three teeth each. The teeth (fig. 4) present slight but distinct 

 and persistent difierences from those of L. helicina (fig. 5) and are larger in 

 proportion to the size of the animal. In the median teeth (4a) the hair-like 

 denticulation is longer and extends higher up the sides of the median cusp, which 

 consequently appears to be shorter ; the base is straighter and bears at either end 

 two or more lobes and bulges. The laterals (4b) are less curved than in L. helicina 

 and the denticulation, as in the median cusp, extends higher. In the oldest row of 

 teeth the laterals are very thin (4c) and the base of the median tooth is simpler, 

 without bulges. 



The whole interior of the stomach (fig. 6) is lined with a thin layer of chitin which 

 gives rise to five stomach plates and also to various prominences and spines (6a) 

 which are larger in the cardiac portion, but do not form four definite accessory 

 plates, such as some authors have reported in L. helicina. The four large stomach 

 plates (fig. 6a) consist of a rectangular or oval base out of which rise one or more 

 prominences with strongly jagged edges. These plates appear to play on one another, 

 which probably modifies the details of the shape in each case : in two the point of 

 the projection is more acute and more bent than in the others. When the four pro- 

 jections are in contact a conical hollow remains between them posteriorly and into 

 this fit the prominences of the fifth plate (fig. 6a, e), which is smaller than the 

 others and lies below them on the pyloric wall of the stomach, but is of essentially 

 the same form, though generally seen sideways and hence apparently more triangular. 

 In all the specimens examined the stomach was found to contain globigerina and 

 diatoms. 



The inner whorls of the shell are entirely filled with the white hermaphrodite 

 gland. 



Authorities are not agreed whether this form is a separate species (Pelseneer) 

 or a variety of L. helicina (Meisenheimer). In the hope of contributing to a 

 decision, I have compared with the 'Discovery' collection a large number of 

 specimens kindly furnished me by Professor D'Arcy Thompson, C.B. (from Davis 



