PLEUROTOMARIA. 423 



Bibliography, Sfc. — Deslongcharnps had some doubt whether his PL "reticulata" 

 was really distinct from PL textilis., which latter, likewise, was held to merge into 

 PL " scalaris." It must be admitted that these three forms wait upon each other 

 closely, and I am inclined to regard PL " scalaris " as merely a megalomorph of 

 PL textilis. PL " reticulata " seems distinct, but as the specific name had already 

 been appropriated, the species was re-named subreticulata by d'Orbigny. 



Description. (N.B. — There are two forms or varieties of PL subreticulata. in the 

 Dorset beds. The following more particularly relates to the narrow, elongate 

 variety from the Humphriesianus-zone — fig. 6 :) 



Height . . . . .36 mm. 



Basal diameter . . . .28 mm. 



Spiral angle ..... 55°. 



Shell conical-elongate, not umbilicate. Spire regular, with a sharp apex. 

 Whorls (nine or ten) flat to subangular, with a slight basal rim ; sutures rather 

 close. The entire shell, including even the sinus-band, is finely and evenly 

 reticulate. 



The sinus-band, which has three spiral lines, is rather below the middle of the 

 whorls, prominent but not very wide; it forms a keel, and thus, in conjunction 

 with the basal rim, causes the whorls to be slightly bicarinate. Body-whorl 

 distinctly bicarinate, the upper keel being formed by the sinus-band ; sharply 

 angular at the periphery, with a flat base. There is a slight umbilical fissure but 

 no true umbilicus. Aperture almost square, with a straight inner lip. 



This variety occurs at Louse Hill and Mapperton ; the former locality yields 

 fossils of the Humphriesianus-zone. The precise horizon at Mapperton has not, to 

 my knowledge, been exactly determined, but the Gasteropoda greatly resemble 

 those from Louse Hill. 



Description of a smaller variety from the ParLiusotii-zoue : — Short, conical shells 

 about 20 mm. in height, and with a spiral angle of 60°. These approach PL 

 distinguenda, Tawney, but are more bicarinate, whilst the ornamentation is 

 more reticulate than in that species. The aperture is very square, and the 

 inner lip thickened and slightly recurved. I have four specimens from the bed 

 distinguished as P. 1, Burton Bradstock. 



Relations and Distribution. — PL subreticulata, besides its intimate relation with 

 the species next described, is connected with a kind of sequence of reticulate 

 Pleurotomarim which are found on more than one horizon in the British Jurassic 

 rocks. Tawney recognised this species from the Dundry beds ; in Dorset it is 

 only found in the Upper Division of the Inferior Oolite. 



A specimen from the Lincolnshire Limestone of Rauceby (fig. 7) is 

 provisionally referred to PL subreticulata. It differs from the Dorset shells (long- 

 type) in its wider spiral angle and less bicarinate whorls. The axial lines or 



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