PLEUROTOMARIA. 415 



Relations and, Distribution. — The oblique and sinuous radial ornamentation in 

 the upper part of the whorls resembles that which characterises both PL sulcata and 

 PL Agathis. But the conical outline and sharper apex distinguish it from both 

 these species. The general form is undoubtedly near to PL unisulcata, though 

 somewhat too uniformly conical, and the whorls not sufficiently angular. 



I have six specimens from the Humphriesianus- zone of Louse Hill and Oborne. 

 The exact locality of the figured specimen is unknown (? Louse Hill). The form may 

 be regarded as representing PL sulcata, Sow., on a higher horizon, and very nearly 

 equivalent to PI. unisulcata,, d'Orb. 



353. Pletjkotomakia (? Leptomaria) Amyntas, d'Orbigny, 1850. Plate XXXV, fig. 12. 



1850. Pleueotomaria Amyntas, d'Orbigny. Prod., i. p. 268. 



1854. Terr. Jur., vol. ii, p. 495, pi. 



cccxcii, figs. 6 — 10. 

 1873. — — — Tawney, Diiudry Gasteropoda, 



p. 41 (33). 



Description : 



Height . . . . .44 mm. 



Basal diameter . . . .44 mm. 



Spiral angle ..... 55°. 

 Shell smooth, conical, subelongate, with a deep but narrow umbilicus. Spire 

 regular and sharp, with the apex rather flattened. Number of whorls about 

 nine in fully-developed specimens, though eight is more usual ; these are sub- 

 angular and moderately convex. The ornaments are usually very fine ; in well- 

 preserved specimens it is seen that the spiral striae in the apical whorls are crossed 

 by fine axial lines, so as to be subreticulate ; later, the spiral ornamentation 

 becomes feeble ; the body-whorl in most specimens is nearly smooth, though in 

 some (such as the one figured) the spiral ornaments are still visible. 



The slit is narrow, and extends backwards about a quarter of the circumference 

 of the body-whorl. The sinus-band is narrow and smooth, being situate on the 

 angular prominence of each whorl, so as to constitute a slight keel about two- 

 thirds the way down. The body-whorl is usually smooth and bluntly angular at 

 the basal periphery, the base flat, and glabrous or substriated ; umbilicus funnel- 

 shaped. Aperture suboval. 



Relations and Distribution. — This fine and often glabrous shell has affinities 

 with the typical Leptomariae through its narrow sinus or slit ; whilst the size and 



54 



