SCISSURELLA. 53 



This differs from any other species known to me in being devoid 

 of sculpture, and in having a conspicuous umbilicus. (Jeffreys.) 



Seissurella umbilicata JEFFREYS, P. Z. S. 1883, p. 88, t. 19, f. 1. 

 S. TENUIS Jeffreys. 



Shell forming a depressed cone with an expanded base, sloping to 

 the periphery and slit, very thin, scarcely transparent, and rather 

 glossy ; sculpture, extremely numerous and fine curved longitudinal 

 striae, and equally numerous and fine concentric or spiral striae, which 

 by their intersection cause a regular but minute cancellation; the 

 concentric striae at the base are stronger and more distinct than the 

 longitudinal striae ; the sculpture is of course interrupted by the 

 peripheral slit and groove ; color pearly white ; spire greatly depressed ; 

 whorls 5, somewhat flattened below the suture ; the last enormously 

 exceeds in size all the others put together ; slit central, long and 

 broad; groove also broad, marked across by regular but rather 

 distant curved striae ; edges sharp and upturned ; mouth obliquely 

 oval ; outer lip thin ; inner lip folded back and curved ; pillar 

 nearly straight, having a twisted fold in front of the umbilicus, which 

 is small and narrow. Alt. 0'25, diam. 0'2. (Jeffreys.} 



North Atlantic. 



This differs from S. crispata and its varieties in its depressed shape, 

 thinner texture, more delicate sculpture, the larger size of the last 

 whorl in comparison with the others, the pillar being furnished with 

 a fold, and in its narrower umbilicus. (Jeffreys.') 



Stissurella tennis JEFFREYS, Ann. and Mag. Nat. Hist., 4th series, 

 vol. 19, p. 234. 



S. CONICA d'Orbigny. PI. 57, figs. 8, 9. 



Shell orbicular-conic, globulose, pellucid, transversely lamellose- 

 ribbed ; spire elevated ; carina wide ; aperture rounded ; umbilicus 

 large. Alt. 2 mill. (Orb.) 



Falkland Is. 



S. conica ORB., Voy. dans 1'Amer. Merid., p. 470, t. 78, f. 7-9. 

 PHILIPPI, Conchyl. Cab., p. 35, t. 6, f. 4. 



S. BERTHELOTI d'Orbigny. PI. 58, fig. 26. 



Shell orbicular-depressed, vertex a little flattened, transversely 

 striate-costate above, striate below ; spire depressed ; whorls 3, 

 rounded ; carina broad, acute ; aperture orbicular ; lip thin, acute ; 

 umbilicus open. Slit fascicle smooth ; color bistre-brown. (Orb.) 



Teneriffe, Canaries. 



