PILEOLUS. 337 



Genus — Pileolus, G. B. Sowerby, 1823. 



Shell limpet-like above, with a subcentral apex ; concave beneath, with a narrow 

 semilunar aperture, having a raised border and a columellar disc, surrounded by a 

 broad and continuous peristome. Apex not spiral ; shell provided with a columellar 

 septum. 



According to the original diagnosis of this singular genus, Sowerby regarded it 

 as possessed of a short internal spire, and this statement is repeated by Morris 

 and Lycett. There does not seem any reason, however, to suppose that Pileolus 

 possessed an internal spire, although the plications shown in the enlarged section 

 (PI. XXVIII, fig. 16) in the region to the left of the columellar septum are some- 

 what imitative of one. 



Fischer speaks of the apex as being subcentral, not spiral. Mr. B. B. Wood- 

 ward also, in a recent communication to the Zoological Society, 1 observes that 

 this genus most clearly possesses a septum, as in Neritina crepidularia and Tomo- 

 stoma, and that there is no true internal spire. 



270. Pileolus plioatus, G. B. Sowerby, 1823. Plate XXVIII : var. A, figs. 13 a, 



13 b; var. B, figs. 14 a — c. En- 

 larged section, fig. 16. 



1823. Pileolus plicatus, O. B. Sowerby. Genera of British Shells, No. 19, 



figs. 1 — 4. 

 1823. — — J. Sow. Min. Conch., pi. ccccxxxii, figs. 1 — 4. 



1851. — — Sow. Morris and Lycett, Great Ool. Moll., pt. i, 



p. 60, pi. ix, figs. 36, 36 a— c. 

 1854. — — G. Sow. Morris, Cat., p. 268. 



? Syn. Patella costulata, Miinst. Goldf., Petref. Germ., pi. clxvii, fig. 9. 



Bibliography, Sfc. — The type of Pileolus plicatus was obtained from the Great 

 Oolite of Ancliff ; the species is also well known, though far from common, in the 

 Great Oolite of Minchinhampton. Morris quotes both this and P. Isevis from the 

 Inferior Oolite of the same district, and other authors, including Witchell (' Geology 

 of Stroud,' p. 47), make mention of these two species as occurring in the Inferior 

 Oolite of the Cotteswolds. I have not seen specimens from the Cotteswolds, but 

 the specimens from Lincoln, figured in the accompanying plate, differ consider- 

 ably from the form prevailing in the Great Oolite of Minchinhampton. 



1 " On the Mode of Growth and the Structure of the Shell in Velates conoideus, Lamk., and 

 other Neritida?," 'Proc. Zool. Soc.,' June 14th, 1892. 



