1873.] MR. R. B. WATSON ON MADEIRAN MOLLUSKS. 377 



base ; from R. macandreivi in the number and narrowness of its 

 longitudinal ribs, the greater depth of the suture, the greater swell 

 of the whorls, the finer and more mucronated spiral threads, stain on 

 apex and on lower lip corner ; from R. watsoni in greater size, 

 especially of upper whorls, stronger and more regular ribs, stain on 

 apex ; from R. nocarensis in being smaller, less tumid, less brilliant, 

 ribs much fewer, spiral threads fewer and more strongly marked on 

 the ribs, spire rising in steps. 



7^ £1^ Rissoa novarensis, Watson. (Plate XXXV, fig. 13.) 



Shell conic-oval, not rising in steps, somewhat solid, glossy, 

 brilliant, subopalescent. 



Sculpture. Longitudinal ribs, from 20 to 30, narrow, flexnous, 

 about as wide as their intervals, diminishing in number on upper 

 whorls and dying out on base. Labial rib thick and strong. 

 Spiral threads on body-whorl about 14 ; they are slightly broader 

 below than above periphery, where they are sometimes evanescent ; 

 they are about twice as broad as their interstices. Six of these 

 usually appear on the penultimate whorl, but they become too 

 indeterminate for counting. They are always most distinct in 

 the rib-intervals ; on the rib-crests they tend to evanesce. Besides 

 these, the whole surface is covered with faint longitudinal lines ; and 

 on the upper whorls especially exceedingly fine microscopic spiral 

 lines can sometimes be traced. On the embryonic \\ whorl about 

 twelve closely and finely stippled spiral lines are visible. 



Colour yellowish white, opalescent on ribs, with three broad 

 irregular and interrupted bands or series of spots of a clear yellowish 

 brown, darkest near tne mouth. The first is below the suture, the 

 second at the periphery, the third on base. The first and second 

 tend to coalesce behind the labial rib, at which point the third series 

 also expands, crossing the rib and staining the lower outer corner of 

 the mouth, the whole outer edge of which has a tinge of brown. 

 The belly is yellow, and the whole pillar and labial rib an opaque 

 white. The tip of the embryonic shell is a rich deep chestnut- 

 brown. 



Spire a short broad cone, terminating in a blunt flattened apex in 

 the centre of which the brown tip swells into sight. 



Whorls 4 to 5, very much flattened so as to form a continuous 

 straight slope from tip to periphery, of rather rapid increase. 



Suture straight, shallow, narrow, but very distinct. 



Mouth oval, very little pointed above, contracted on its outer 

 upperside, but expanded on base. 



Outer lip thickened by a heavy white rib, somewhat incurved 

 above, and there bevelled off from the outside to a sharp edge, 

 whereas on the base the bevelling-off is from the inside entirely. 

 This labial rib lies a little way back from the edge ; and beyond it 

 the sharp mouth-edge is only scored by fine longitudinal lines. 



Inner lip is barely detached from the pillar, so as to leave a slight 

 chink ; it is continued pretty thickly across the belly, and meets 

 the outer lip in a rounded and somewhat padded angle. 



