164 GASTROPODA. [Aspidobranchia. 



Genus 2. LEPTOTHYRA, Dall, 1871. 



Leptothyra, D.,11, Amcr. Journ. Conch., vii, 130. Type: Turbo sanguine us, L. 

 Leptonyx, Carpenter and A. Adams, Proc. Cal. Acad. Sci., iii, 1864, 175 ; 

 not of Gray, 1837 (Phocidce). Collonia, Philippi, Handbuch d. Conch., 

 200, not of Gray. Collonia (sp.), H. and A. Adams, Gray, Watson, &c. 



Radula : The median teeth are oval, wide, with a narrow pro- 

 jection above, and more or less narrowed toward the base ; the upper 

 margin is in no case reflected, so that cusp, cutting-point, or edge, in 

 any usual sense, there is none. 



Shell small or minute, globose-depressed, solid, compact, umbilicate 

 or imperforate ; whorls 3-7, spirally sculptured, the last generally 

 somewhat deflexed at the aperture ; aperture subcircular, white and 

 nacreous within ; columella generally, but not always, bluntly den- 

 ticulate near the base. Operculum subcircular, nearly flat or concavo- 

 convex, inside with a very thin corneous layer, slightly convex, with 

 many gradually increasing whorls, the nucleus subcentral, outside 

 calcareous, subspiral, with a slightly convex concentric elevation or 

 ridge around the margin, most prominent at its termination, the 

 middle portion concave and more or less rugose. 



The species are numerous, inhabiting nearly all tropical and sub- 

 tropical seas, but most numerous in the Pacific. 



Fossil. Tertiary. 



KEY TO SPECIES. 



A. Shell closely spirally lirate, the lirae numbering 25-35 on the 



last whorl . . . . . . . . . . . . fl,uctuata. 



B. Shell strongly spirally ribbed, the ribs numbering 1220 on the 



last whorl . . . . . . . . . . . . crassicostata. 



1. Leptothyra crassicostata, Murdoch, 1905. Plate 34, fig. 10. 



Leptothyra crassicostata., Murdoch, T. N.Z.I., xxxvii, 1904 (1905), 223, pi. 7, 

 f. 11. 



Shell small, solid, turbinate, umbilicate, with strong variable 

 spiral sculpture. Sculpture : The penultimate whorl with 3 to 5, 

 the last with 12 to 20 spiral ribs. The ribs are very variable in size : 

 there are 5 to 8 strong riblets between the periphery and suture on the 

 body-whorl ; in front of the aperture 4 or 5 about equal to the breadth 

 of the interspaces ; on and immediately below the periphery the 

 cinguli are frequently small and crowded, and similar on the base, 

 or there may be 2 or 3 more prominent cinguli intercalated with the 

 smaller ones, or the basal riblets may generally be stronger than those 

 on the periphery ; the growth-lines are strong and irregular, producing 

 here and there a lightly costate appearance, frequently well pro- 

 nounced in the umbilical area. Colour whitish or light brown, occa- 

 sionally with irregular markings of brown, most distinct on and 

 below the periphery. Spire low, rounded. Protoconch minute, smooth. 

 Whorls 4, flattened below the suture, then convex, rapidly increasing ; 

 base convex. Suture impressed. Aperture subrotund, white inside. 



