600 THE VOYAGE OF H.M.S. CHALLENGER. 



patulous. Inner lip quite continuous with the outer lip, thin, defined, short on the body, 

 thin, curved, patulous on the pillar, where behind it is a strong furrow and umbilicus, 

 which it half covers. H. 0-051 in. B. 0'41. Mouth, height 0'025, breadth 0"023. 



In sculpture this species very much resembles Rissoa moniziana, Wats., but is much smaller and 

 stumpier in form, is umbilicated, the base is less produced, and the whorls are rounder. 



25. Rissoa (Onoba) aedonis,] n. sp. (PI. XLV. fig. 5). 



Station 135c. October 17, 1873. Lat. 37° 25' 30" S., long. 12° 28' 30" W. Off 

 Nightingale Island, Tristan da Cunha. 100 to 150 fathoms. 



Shell. — Strongish, oblong, conical, subtransparent white, with a blunt rounded tip, 

 subscalar spire, round striated whorls, an impressed suture, a rounded base, an unvarixed 

 lip, and an ovate mouth. Sculpture : Longitudinals — there are feeble irregular unequal 

 lines of growth. Spirals — there are strongish distinct spiral threads (about nine on the 

 penultimate whorl), parted by squarish furrows of about double the breadth of the 

 threads; these furrows are exquisitely fretted by very minute close-set microscopic 

 scratches, which give a beautiful crispness to the surface. Colour translucent white. 

 Spire rather high and subscalar. Apex gibbously rounded and smooth, having no sculp- 

 ture. Whorls 5, rounded, the last long and large in proportion to the rest. Suture 

 impressed, very slightly oblique. Mouth round, but a very little narrowed above. Outer 

 lip sharp, thin, well rounded in its whole curve, patulous, with a slightly prominent edge. 

 Inner lip thin on the body, but well defined, curved, patulous and appressed on the 

 pillar. H. 0-09 in. B. 0-05. Mouth, height 0-04, breadth 0'033. 



The delicate microscopic spiral fretting of this species resembles that which may be seen in 

 Rissoa striata, Adams. 



26. Rissoa (Onoba) mercurialis, 2 n. sp. (PL XLV. fig. 12). 



Station 186. September 8, 1874. Lat. 10° 30' S., long. 142° 18' E. Off Wednesday 

 Island, Cape York, North-east Australia. 8 fathoms. Coral mud. 



Shell. — Large, long, and high, pure white, spirally striate, blunt tipped, convex 

 whorled, with a slightly impressed oblique suture, long body-whorl, produced base, and 

 roundly oval mouth. Sculpture : Longitudinals— the whole surface is pretty closely scored 

 with slio-ht unequal lines of growth, some of which are mere scratches, while others are 

 feebly raised and rounded. Spirals — there are on each whorl many small close-set threads 

 and furrows ; the threads are flat and very little raised, and the furrows resemble them 



1 aribuv, a nightingale. 2 So called from the island off which it was found. 



