50 SCISSURELLA. 



S. COSTATA d'Orbigny. PL 50, fig. 1. 



Shell thin, transparent ; spire depressed, composed of 4 whorls 

 plane on their upper surfaces, strongly carinated at the periphery, 

 convex below the carina ; last whorl very large, widely umbilicated ; 

 aperture oblique, subquadrangular ; columella simple, arcuate ; lip 

 simple, sinuous, with a narrow profound fissure ; slit fascicle forming 

 the carina of the whorls, with elevated, lamellar edges, and arcuate 

 growth-lamellae ; umbilicus broad and deep, carinated at the border ; 

 surface sculptured with arcuate longitudinal riblets, widely spaced 

 and a little undulating, and fine spiral striae ; color white. 



Alt. 1, diam. H mill. 



Mediterranean and Adriatic Seas ; Madeira; Teneriffe, Canaries. 



S. costata ORB., Mem. Soc. Hist. Nat. Paris i, p. 340, t. 23, f. 2, 

 1823. CHENU, Manuel, f. 2716. WEINKAUFF, Conchyl. des Mitt- 

 elm, ii, p. 385. DE FOLIN, Les Fonds de la Mer i, p. 266. 

 JEFFREYS, Proc. Zool. 1883, p. 89. MONTEROSATO, Norn. Gen. e 

 Spec., p. 39. BUQ., DAUTZ., and DOLLF., Moll, du Rouss., p. 430, t. 

 51, f. 8-11. S. Icevigata ORB., loc. cit. supra, p. 340, t. 23, f. 1. 

 Argonanta uniumbilicatus O. G. COSTA, Test, e Crust. Micros., t. 10, 

 f. 1, 1828. plicata PHIL., Enum. Moll. Sicil. i, p. 187 ; ii, p. 159, 

 t. 25, f. 18. S. d' Orbignyi SCACCHI, Catal. Conch. Reg. Neap., p. 16, 

 l&SG.Padollus orbignyi O. G. COSTA, Catal. Taranto, p. 51, 1839. 

 Delphinula calcaroides CANTRAINE, Bull. Acad. Bruxelles ix, p. 

 341, 1842. S. cancellata JEFFREYS, Piedm. Coast, p. 27, f. 1. S. 

 affinis O. G. COSTA, Microd. Medit., p. 60, t. 10, f. 2. S. decipiens 

 COSTA, 1. c., p. 60. S. striatula PHIL., Enum. Moll. Sicil. ii, p. 160 ; 

 Conchyl. Cab., p. 37, t. 6, f. 9. 



Var. L^EVIGATA Orb. PL 50, fig. 2. 



Longitudinal riblets entirely wanting. 



The name Icevigata really has priority of costata, and if, as the 

 authors of Mollusques du Roussillon state, the two forms are con- 

 nected by imperceptible gradations, Icevigata should be taken as the 

 typical form, of which costata is a variety. In nature, however, the 

 reverse is doubtless the case. 



S. DORBIGNYI Audouin. Vol. XI, pi. 67, figs. 85, 86, 87. 



The shell is thin, transparent, glassy, white, ovate, rather de- 

 pressed, consisting of 3 rather rapidly increasing whorls, and has a 

 very peculiar sculpture ; under the rather elevated slit fasciole there 

 are two elevated line, and the base has concentric lirse and grooves, 



