591 KEY. R. BOOG WATSON ON THE 



Shell. — Thin, white, opalescent, smooth, faintly reticulated. In 

 form slightly resembling a smallish Zonites cellariuSj with a 

 high concave spire, sharp apex, acute carina, angulated umbi- 

 licus, and rhomboidal mouth. Sculpture. Smooth, glossy, irides- 

 cent, with ten to twenty faint spiral threads on the upperside of 

 the body-whorl ; the last of these which joins the lip is much 

 stronger than the others ; a little remote and below is a thread 

 forming the keel, below which, and nearer, are two other strong 

 threads ; round the umbilicus are also two strong threads ; the iu- 



• termediate space on the base is marked with eight to ten im- 

 pressed spiral striae. The interstices of the spirals are crossed by 

 longitudinals, which are regular, fine, hair-like, but distinct and 

 well parted ; their curve on the surface below the suture shows 

 the old sinus. On the base they are radiating and are crowded 

 and irregular, except round the umbilicus, where in the first 

 two or three striae they are very sharp and distinct. On 

 the upper whorls both the spirals and longitudinals are finer, 

 but sharper, than on the last. Colour a greyish, horny, trans- 

 lucent, opalescent white. Spire raised, with a concave outline. 

 Jpeo!, which consists of the single minute embryonic whorl, is 

 slightly exserted and sharp ; it is quite smooth, but the spirals and 

 longitudinals begin sharply immediately below it. Whorls 6|, of 

 slow and regular increase except the last, which widens rapidly, 

 depressed, quite flat, except the last, which is slightly rounded 

 above, and still more slightly concave on the base, with an acute, 

 but still* rounded keel. Suture impressed on the body -whorl, 

 but on the upper whorls sharply, though slightly, marginated 

 below. Mouth a little oblique, rhomboidal, the basal and palatal 

 lines being nearly parallel, while the outer and inner lip diverge 

 dowjiwards. Outer lip thin, not patulous, not descending, advan- 

 cing at its junction with the body-whorl, and then retreating so as 

 to form a shallow, broad, open sinus a little below the suture, 

 acutely, but roundedly, angulate at the periphery, nearly flat on 

 the base, with a very slight nick at the point of the pillar, where 

 it joins the inner lip at a slightly obtuse angle. The pillar-lip is 

 straight. It is a very little thickened, and is slightly porcella- 

 nous. It advances a little on the edge of the umbilicus ; below 

 this it is hollowed out by a receding curve, but advances again 

 into a slight rounded projection just above its junction with the 

 outer lip. In its whole direction it inclines slightly to the left. 

 Umbilicus oblique edged, funnel-shaped, being wide in the 



' mouth and deep, with straight converging sides. It is slightly 



