GODWIJf-ATJSTEN : ON TROCnOIfANIN'A, ETC. 235 



knowledge of the Land Mollusca, and is well illustrated. The 

 radula is similar to that of the species I am now describing ; the 

 jaw, however, has no central projection. He also describes H. 

 costulata, . Von Martens, which has a similar jaw, but differs 

 in its radula, in which, though the centrals are still plain 

 straight-sided teeth, the outermost laterals at the 20th and 21st 

 tooth are curved and unilinear. He has placed them both in 

 Trochomorpha. The formulae for their radulae are — 



77". planorhis 39 : 10 : 1 : 10 : 39 

 49 : 1 : 49 



H. costulata 38 : 10 : 1 : 10 : 38 

 48 : 1 : 48 



Differences, similar to those noted above, separate these two species 

 from Sivella cadra, and they fall naturally into Discus. 



1. Discus trilineatus. 



Hah. — Great Mcobar (De Rocpstorff). 



Animal. — Has no overhanging lobe at the extremity of the foot : the 

 slit of the mucous gland can not be discerned owing, possibly, to the 

 contracted state of the spirit specimen, though the wide pallial fringe 

 and the shape of the extremity of the foot point undoubtedly to its 

 presence. The animal is black in colour, with a pale foot beneath, 

 and above the pallial margin is finely papillate. The jaw has a 

 central projection. The radula (Fig. 2^) has the teeth arranged 

 -|-9: 11: 1:11:9+? It was unfortunately imperfect on both 

 the lateral sides, where the teeth are very small. The twenty-two 

 centrals are plain straight-sided teeth, the centre tooth not so broad 

 as those on either side ; the laterals are curved, short, and evenly 

 bicuspid. 



The generative organs (Fig. 2). — The vas deferens joins the male 

 organ below the retractor muscle attachment, and at its junction is 

 closely coiled upon itself (Fig. 2a) ; this was seen in two specimens 

 dissected. The spermatheca is only of moderate length, and thus 

 these organs have a very distinct construction to that which 

 IStoliczka describes in Sivella castra. The other parts of the 

 generative organs do not call for any special mention. 



2. Discus hicolor. — Borneo (A. Everett). 



Animal. — Jaw not seen, probably like that of D trilineatus. The 

 central teeth of the radula are plain, straight-sided, as in D. trilineatus • 

 the outermost are, moreover, short and evenly bicuspid, becoming 

 very minute on the edge ; the formula being — 



30 : 2 : 10 : 1 : 10 : 2 : 30 

 or 42 : 1 : 42 : 



The generative organs (Fig. 3) do not materially differ from those of 

 the last described species ; the muscular attachment is above that of 

 the vas deferens ; the spermatheca is rather short and elongately club- 

 shaped. 



Since writing the above, I have seen the Manual of Conchology, 



