153 



Note on the Presence of the Fossil genus Isodonta, Buv., in the 

 English Jurassic Rocks. By JOHN LYCETT, Esq. 



To James Buckman, Esq., Hon. Sec. to the Cotteswold 

 Naturalists 9 Club. 



DEAR SIR, 



Will you have the goodness to communicate to the Club, at 

 their next meeting, that we may claim the genus Isodonta, Buv. 

 (Sowerbya, D'Orb.), as an addition to the fauna of the English 

 Jura ? 



The sole species hitherto described is the Isodonta Deshaysea, 

 Buv., from the ferruginous Oolite of the Oxfordian beds of the 

 Department of the Meuse. Recently, my good friend Mr. 

 Leckenby presented me with a fine specimen of the so-called 

 Cucullaa triangularis, Phill., from the Cornbrash of Scarborough. 

 The resemblance in the general aspect of this shell to the Iso- 

 donta of Buvignier was at once apparent ; but it was only upon 

 an inspection of specimens in the British Museum, collected by 

 M. Tesson, that their identity with the Yorkshire shell became 

 a conviction to my mind. Individual specimens vary in their 

 elongation and in the degree of angularity at their infero-pos- 

 terior extremity : little differences of this kind form the sole 

 distinction between the British fossil and that of the Meuse, 

 and the Normandic specimens in the Museum differ from each 

 other at least to an equal extent. The Cucullaa triangularis, 

 Phill. Geol. York. i. tab. 3. fig. 31, is from the Coralline Oolite 

 of Malton ; it is somewhat less elongated than my Cornbrash 

 specimen, and agrees more nearly with the figures of Buvignier, 

 ' Paleont. de la Meuse/ Atlas, pi. 10. figs. 30-35, except that 

 the figure of Phillips is somewhat more inequilateral from the 

 shortness of the posterior slope : in the Cornbrash specimen, as 

 in those from Normandy and from the Meuse, this feature is 

 less conspicuous ; but there can be no doubt that the anterior 

 side is always somewhat more produced than the other; the 

 surface is smooth, but with two distant and strongly-marked 

 folds of growth. The very tumid figure and incurved umbones 

 are the external characters whereby it may be distinguished 

 from Tancredia ; the test is likewise thicker than in the latter 

 genus. At present it does not seem that the Cornbrash shell 

 can be separated as a species either from that of the Yorkshire 

 Coralline Oolite, from the Normandic specimens, or from those 



