PLEUROTOMARIA. 423 
Bibliography, §c.—Deslongchamps had some doubt whether his Pl. “ reticulata” 
was really distinct from PI. tevtilis, 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” 
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 
as merely a megalomorph of 
variety from the Humphriesianus-zone—fig. 6 :) 
Height : re : : SSO Mmme 
Basal diameter ; : : . 28 mm. 
Spiral angle . eo. 
- 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, imcluding 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 Parkinsoni-zone :—Short, conical shells 
about 20 mm. in height, and with a spiral angle of 60°. These apprcach PI. 
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 
Plewrotomariz 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. ‘he axial lines or 
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