MOLLUSCA OF INDIA. 95 



The dental formula is — 



204 . 23 . 1 . 23 . 204 

 227 . 1 . 227 



The jaw (fig. 7) is by no means strongly or solidly developed ; it 

 has a simple slightly concave cntting-edge. There is no defined 

 upper margin ; this edge merges into the muscular tissue : or, in 

 other words, the jaw does not come away in one solid mass, as it 

 does in most other species of the Zonitida3. 



This type of odontophore is seen in Hemiplecta uter, Theob., and 

 H, Jmmjjhreysiana, Lea, only that the breadth of the radula is 

 greater in the Ceylon mollusc, there being 160 more teeth in the 

 row. The jaw is also without the central projection in those two 

 species. 



The f/enerative system (figs. 6, 6 a). There is a large amatorial 

 organ, having a sharp S-like bend, near the genital aperture. The 

 male organ is very simple — a moderately long sheath, with a large 

 bulbous swelling, to which the vas deferens is connected ; a long, 

 solid sheath continues above this, to which the retractor muscle is 

 attached. This bulbous swelling represents the kalk-sac in a very 

 shortened form, and is probably continued in a bend within the 

 solid sheath, which represents the ccecum musculi retraetoris penis 

 of Semper. 



Compared with Cryptosoma (Plates IV. & LXX.-LXXII.), there 

 are many important differences in the radula and jaw, in the form 

 of the amatorial and male organs, and particularly in the sole of 

 the foot. I have noticed that in many of the Cingalese species the 

 foot, after preservation in alcohol, contracts upon a central line, 

 which is never the case in Macrochlamys, Girasia, &c. This indi- 

 cates, I think, that similar contraction prevails in life, and perhaps 

 points to an arboreal habit of the animal. The two genera last 

 mentioned are essentially terrestrial, and are not to be sought for, as 

 a rule, on shrubs far above the ground, although occasionally in very 

 wet weather they may some of them be found there. 



Cryptosoma insusitatum, in the form of the dart (Plate LXX. 

 figs. 7 h, 7 c), shows a decided approach to the Malayan Micro- 

 parmarion, only it has not become calcareous, but it is protrusive to 

 a considerable extent. 



Still greater differences may be noted between R. irradians and 

 BurgeUa ch'istianue (Plate LXXIX.), as also when it is placed 

 beside the South-Indian forms, such as DurgelJa dekhanensis 

 (Plate LXXVIII.). I therefore consider a new subgenus must be 

 created for it, and that the grounds for doing so are sufficient. 



Description of subgenus Hatnadvipia. 



(The old Sanscrit name of Ceylon, compounded of 

 " Ratna," a jewel, " Dwip," an island.) 

 Animal. The right shell-lobe is in two parts ; above, near the 

 respiratory orifice, a tongue-shaped process i)lays over the uj)per 



