EXELISSA. 177 



10G. Ceritella Lindonensis, sp. nov. Plate XI, figs. 3 a, 3 b, 4. 



Description. — Length from 8 — 10 ram., with an average width of about three- 

 eighths of the height, but varying considerably ; mean of spiral angle about 30°. 

 Shell turrited, apex acute ; whorls about eight, flat, smooth, and increasing 

 suddenly by steps ; shoulder somewhat sloping, marked with a spiral line below 

 the suture, producing a sort of zoned appearance in some specimens. 



Body-whorl large, fully equal to half the entire length of the shell, smooth, 

 cylindrical, slightly constricted in the centre, and rounded at the base. Columella 

 long, slightly arcuate, and reflexed ; aperture elongate, and anteriorly oblique, 

 terminating in a sort of tube which has very much the appearance of a canal. In 

 section the outer wall of the whorls is perfectly smooth, but a slight tendency to a 

 fold may be noticed on the columellar side. 



Relations and Distribution. — The impressed line on the shoulder, the large rela- 

 tive size and cylindrical shape of the body-whorl, clearly distinguish this species 

 from G. acuta, M. and L. It is much more nearly allied to G. Sowerbyi, M. and L. 

 Indeed, there are specimens in the Great Oolite of Minchinhampton which can 

 hardly be said to differ from some of those in the Lincolnshire Limestone. But G. 

 Sowerbyi, as figured and described, has not the body-whorl quite so cylindrical or 

 so large. In fact G. Sowerbyi is not quite so like a Nerinsea. 



The varieties of C. Lindonensis are considerable. Figs. 3 a, 3 b, represent a front 

 view and a section of a short stout form, which might lead to a different species. 

 It is rare. Fig. 4 represents an unusually large specimen of the more prevailing 

 form, which occurs sparingly at Weldon. The small, slender forms from Ponton 

 are almost identical with C. Sowerbyi. Indeed, the less completely developed 

 specimens, whether from Ponton or from Weldon, are not to be distinguished 

 from ordinary forms of the Great-Oolite species. 



Genus— Exelissa, Piette, 1361, « Bull. Soc. Geol. France, 2 me air., t. 18, p. 15 ; 

 := Kilvertia, Lycett, ' Supplement,' pp. 15 and 93. 



" Shell small, narrow, subcylindrical, somewhat pupseform ; whorls numerous, 

 ornamented, with longitudinal ribs, tuberculated or spinous ; last whorl contracted at 

 the base, with a tendency to detach itself from the axis ; aperture orbicular, entire, 

 with lips elevated, prominent, slightly thickened ; columella solid." — Fischer. 



With few exceptions, the above is the original diagnosis of Kilvertia, which was 



23 



