1891.] LAND-SHELLS FROM BORNEO. 29 



closing towards the posterior end and contracted for a short distance 

 into a tube, the retractor muscle being at the junction of the vas 

 deferens. The spermatheca is very and unusually long, extending 

 to the albumen-gland ; it rises from anotlier pear-shaped muscular 

 sac, on the side of which the oviduct enters. There is nothing 

 remarkable about the ovo-testes or albumen-gland. 



The odontophore (Plate VI. fig. 8). — The form of the median teeth 

 very gradually merges into that of the laterals, which become at 

 last little short straight teeth. The central teeth are all unicuspid, 

 the central tooth of all being triangular in form ; the formula is 



109 . 43 . 1 . 43 . 109 

 152 . 1 . 152. 



The lingual ribbon I extracted is nearly perfect, not a row was 

 lost, and it contains 177 rows, giving the enormous number of 

 54,000 teeth. 



The jaw (Plate VI. fig. 7) has a low central projection, and is not 

 much bent. 



The character of this animal differs so widely from those in 

 genera with which it is now associated that it does not seem at all 

 in the position it should occupy, and with R. ovum and others will 

 have to be moved. As I have only been able to obtain one example 

 of R. brookei in spirit, it is better to wait until others are examined 

 before doing so. 



Nanina (^Ryssota) borneensis. 



Helix borneensis, Pfeiff. P. Z. S. 1849, p. 127; id. Monogr. 

 Helic. iii. p. 70 (1853), et. v. p. 114 (18fi8) ; Reeve, Conch. Icon, 

 pi. cxcvi. fig. 1379 (1854). 



Nanina borneensis, v. Martens, P^euss. Exped. Ost-Asien, 

 Landschneck. p. 238. 



Dyakia, gen. nov. (Type, Helix hugonis, Pfeiff.) 



No shell-lobes to the mantle, and the dorsal lobe much reduced in 

 size. Shells generally sinistral. Hitherto placed in AriophantU. 

 The amatorial organ of peculiar form, with a calcareous dart or 

 sagitta amatoria. For further description of details see D. hugonis. 



Dyakia hugonis. (Plate V. figs. 5-5 b.) 



Helix hugonis, Pfeiff. P. Z. S. 1863, p. 523; id. Novitat. Conch, 

 iii. pi. Ixxiv. figs. 1,3; id. Monogr. Helic. v. p. 81 (1868). 



Helix sinistra. Bonnet, Rev, Zool. 1864, p. 67, pi. v. fig. 2. 



Nanina (Hemiplecta) hugonis, v. Martens, Preuss. Exped. Ost- 

 Asien, Landschneck. p. 225 (1868). 



The anatomy of Hemijylecta humphreysiana. Lea, from Singapore, 

 the type of the genus, which I have examined and alluded to before, 

 differs widely from that of H. hugonis. 



Hab. Two specimens from Trusan, and one dextral variety from 

 the Niah Hills {A. Everett). 



