MoUusca of the Arabian Sea, dsc. 95 



Hah. At 25 fathoms, in mud, lat. 26° 23' N., long. 

 54°53'E. 



Remarkably delicate and subpellucid in form, this species, 

 with the important exception of the strong columellar plait, 

 recalls Rissoina epentroma^ Melv. The interstices between 

 the ribs are plain and smooth, in which respect it differs 

 from most of its congeners. The apical whorl is hetei'o- 

 strophe, white, vitreous, smooth and bulbiform ; the remaining 

 four whorls are all uniformly delicately straight-ribbed, and 

 are much impressed suturally, thus assuming a gradate 

 appearance. The mouth is ovate, within spirally striate ; 

 columella with one central strong plait. 



PyrguUna glycisma *, sp. n. (PI. I. fig. 16.) 



P. testa ovata, Candida, compressa, apice globulari, Isevi, hefcero- 

 stropho ; anfractibus (apicalibus 1| inclusis) 6|, ad suturas im- 

 pressis, paullum gradatis, longitudinaliter arete obliquicostatis,. 

 costis laevibus, crassiusculis, nitidis, interstitiis delicate spiraliter 

 striatis, ultimo anfractu ad peripheriam spiraliter profande cana- 

 licLilato et radiatim costulato ; apertura ovata ; labro simplici, 

 paullum incrassato ; columella uniplicata. 



Long. 3, lat. 1'25 mm. 



Hah. Karachi. 



Only a few examples occurred of this small but character- 

 istic species. Mingled with it, but both in far greater 

 plenty, were two having a superficial resemblance to it, viz. 

 PyrguUna callisfaj Melv., which, originally described from 

 Bombay f, attains at Karachi a far finer condition and size, 

 and Rissoina epentroma, Melv., likewise first reported | from 

 the same place. 



The shell is ovate, pure white, sometimes with a cinereous 

 tinge ; apical whorls 1^, heterostrophe, smooth, globular ; 

 the remaining whorls, 5 in number, are uniformly closely 

 obliquely ribbed, these being shining, smooth, and somewhat 

 thickened, witli the interstices spirally striate ; the sutures 

 are impressed, causing the spire to appear slightly gradate ; 

 the ribs of the last whorl amount to 24. Aperture is ovate, 

 outer lip only slightly thickened, columella once plaited. 

 At the periphery of the last whorl is a deep spiral channelled 

 groove, with a revolving rib at its margin. 



This species has as its nearest congeners P. turhonilloidesj 



* ykvKiijixa, a delicacy. 



t Mera. Lit. & Phil. Soc. Manch. ser. 4, vol. vii. p. 9, pi. i. fio-. 13 

 (189a). 



X Proc. Mai. Soc. vol. ii. p. 110, pi. viii. fig 23 (1896). 



