1884.] MOLLUSCA OF THE 'LIGHTNING ' ETC. EXPEDITIONS. 341 



appearance, only that they are nearly colourless ; at the lower end 

 of each is an irregularly shaped nucleus. The lower end of the 

 rhabdom projects into their substance ; the large size and trans- 

 parency of these cells seems to indicate that they serve as dioptric 

 media. 



2. On the Mollusca procured during the ' Lightning ' and 

 'Porcupine' Expeditions, 1868-70. (Part VIII. 1 ) By 

 J. Gwyn Jeffreys, LL.D., P.R.S., F.Z.S. 



[Eeceived April 30, 1884.] 

 (Plates XXVI.-XXVIII.) 



GASTROPODA {continued). 

 Family XVI. Aclid^e. 

 Apex having a dextrorsal and involute spire. 

 Cioniscus 2 , Jeffreys. 



Shell cylindrical, striated or fluted lengthwise, and sometimes 

 reticulated : spire elongated ; apex blunt and twisted : month oval, 

 contracted. 



Differs from Aclis in the sculpture, apex, and shape of the mouth. 



In 'British Conchology' (vol. iv. p. 102) I proposed the generic 

 name Graphis for the only species which was then known, viz. Turho 

 unicus of Montagu, which may be considered the type of the present 

 genus; but I afterwards (vol. v. p. 210) substituted Cioniscus for 

 Graphis, finding that the latter name had been long previously used 

 by botanists for a genus of Lichens. Out of the four species now 

 known, one of them (C. unicus) inhabits the littoral and laminarian 

 zones, all the other species being deep-water or abyssal. 



1. Cioniscus gracilis 3 , Jeffreys. (Plate XXVI. fig. 1.) 



Shell of nearly equal breadth throughout, thick, semitransparent, 

 and glossy : sculpture, numerous sharp and flexuous longitudinal 

 ribs, which extend to the base ; there are about 25 on the last whorl ; 

 each whorl is angulated or shouldered at the top ; the first whorl 

 and a half, which form the apex, are marked by two slight spiral striae, 

 but are otherwise smooth and polished : colour whitish, with a faint 

 tinge of yellowish- brown : spire very gradually tapering to a blunt 

 and apparently truncated point ; apex somewhat inflected : whorls 

 5g, convex, but rather compressed : suture deep : mouth somewhat 



1 For Part I. see P. Z. S. 1878, p. 393 ; for Part II. see P. Z. S. 1879, p. 553 • 

 for Part III. see P. Z. S. 1881, p. 693 ; for Part IV. see P. Z. S. 1881, p. 922 ■ 

 for Part V. see P. Z. S. 18S2, p. 056 ; for Part VI. see P. Z. S. 1883, p. 87 ; and 

 for Part VII. see P. Z. S. 1881, p. 111. 



2 Resembling a little pillar ; from k'h»v, columna, and i'o-icw, assimulo. 



3 Slender. 



