178 GASTEROPODA OE THE INFERIOR OOLITE. 



so well formulated by Lycett, although Piette's name appears to have the priority. 

 Fischer places this genus with a query under the Cerithiidae. 



These curious little shells are by no means abundant. Exelissa numismalis is 

 described by Tate from the Lower Lias. The ornaments of this species are not 

 very characteristic, and, as usual with Lias specimens, the character of the aperture 

 is not well-defined. Four species were recognised by Lycett in the Great Oolite, 

 one of which, Ex. strangulata, D'Arch., is regarded as the type of the genus. All 

 four are recorded by Cossmann as occurring in the Bathonian of France. 



In the Inferior Oolite of this country there are three if not four species of 

 Exelissa, two of which are closely allied to, and possibly in one case identical with, 

 Bathonian species. 



107. Exelissa strangulata, D'Archiac, 1843, Inf.-Ool. Varieties. Plate XI, figs. 



5 a, 5 b, 6. 



1843. Cerithium strangulattjm, D'Arch. Mem. Soc. Greol. Trance, t. v, p. 382, 



pi. xxxi, figs. 1 a, b. 



1851. — — — Morris and Lycett, Great Ool. Moll., 



p. 31, pi. ix, fig. 18. 



L863. Cerithium ? (Kilvertia) strangulatum, D'Arch. Lycett, Suppl., pp. 8 



and 94, pi. xliv, fig. 2. 



Bibliography, 8fc. — Lycett's figure in the ' Supplement ' is good, showing the 

 straight, thick ribs characteristic of this species. He says (p. 8) : " The present 

 specimen, which agrees more nearly with the example figured by D'Archiac, has 

 seven longitudinal costse, which are conspicuous even to the base." 



Var. Pisolitica (figs. 5 a t 5 h). 



Length about same as in specimens of Ex. strangulata from Eparcy (8 or 9 

 mm.), figure rather more slender, and apex less obtuse. The ornamentation differs 

 considerably. In the var. pisolitica the longitudinal costae are not quite so regular, 

 and straight ; moreover the granulations of which the costas are built up are larger 

 and about half as numerous ; they correspond in fact to four or five spiral lines on 

 each whorl instead of at least eight as in Ex. strangulata. The contracted, pupseform 

 aperture, with its prominent lips, is alike in both ; but this, of course, is a generic 

 feature. 



This variety occurs rarely in the lower part of the Inferior Oolite of the 

 Cotteswold, and chiefly in the Pea-grit. 



Var. Ovalis (fig. 6). 



About 8 mm. in length, this variety is broader than typical specimens from 



