400 GASTEROPODA OF THE INFERIOR OOLITE. 



aperture subquadrate and moderately depressed with a slight columellar notch, 

 not always preserved. 



Var. angusta (Fig. 4). 



This represents a form which may be noted m the Lower Division of the 

 Inferior Oolite, where the spiral angle does not exceed 40°, and in some cases, 

 as in the Opalinus -zone at Drympton, is even less. The specimen figured is 

 from Bradford Abbas (? M urchisonse-zone) . Another specimen (Fig. 5), from the 

 Concarus-hed of Bradford Abbas, presents a wider spiral angle besides some 

 difference of ornamentation. 



Var. near to PI. conoidea, Deshayes (Fig. 6). 



1831. Pleurotomaria conoidea, Deshayes. Coq. caract., p. 181, pi. iv, fig. 4. 



This is a variety with extremely rich sculpture ; the spiral angle in some 

 cases is slightly concave, whilst the sinus-band is very anterior and not at all 

 prominent. 1 These forms occur at Mapperton, Louse Hill, and other places 

 believed to be in the Eumphviesianus-zone. 



Pleurotomaria elongata, Sowerby. Type form (Fig. 7). 



Cf. 1854. Pleurotomaria Pictaviensis, d'Orbigny. Ten-. Jur., vol. ii, p. 510, 



pi. cccxcix, figs. 1 — 5. 

 — — mutabilis, var. ambigua, Deslongchamps. Vol. cit., 



p. 113, pi. xi, fig. 1. 



This is a robust form with spiral angle of about 50°. It more nearly 

 approaches Sowerby's type (one of the three species-types preserved in the 

 British Museum 2 ) than any of the others. In this variety the sculpture is 

 principally seen in the more apical whorls ; the basal rim of the anterior whorls 

 being thick, round, and nearly smooth, whilst the spiral stria? in the whorls 

 themselves are less deeply incised. The sinus-band in the lower whorls is smooth 

 and very anterior ; stria? in the base indistinct. Aperture subquadrate and 

 moderately depressed ; traces of the columellar notch very slight. 



Characteristic specimens occur ;ibundantly at Dundry and in the Saiizei-hed 

 (base of tin' Humphriesianus-zone) at Combe and Oborne. Some persons might 

 be disposed to restrict the specific name, elongata, to this form. 



Mr. Wilson considers that PL conoidea should be regarded as a distinct species, as he attaches 

 great importance to the want of prominence in the sinus-band. 

 - Vide antea, p. 396. 



