2.22 Mr. J. Lycett on the genus Tancredia. 



the past year (1852) a French author of eminence, both as a 

 geologist and palaeontologist, M. A. Buvignier of Verdun, has, in 

 a new and splendid work on the geology of the department of 

 the Meuse, figured and described certain species of Tancredia 

 under the new generic name Hettangia, a name which he states 

 to have been chosen by M. Turquem, the discoverer of the genus. 

 The very superior manner in which the figures of that work are 

 executed leaves no doubt of the identity of the two genera ; the 

 five species which M. Buvignier has illustrated are from the Lias, 

 and bear the specific names Broliensis, Deshayesea, Turquemea, 

 longiscata, and Raulinea ? They are all distinct from the oolitic 

 species of the Cotteswolds. From this statement it is evident, 

 that in the absence of any other notice of the genus, my memoir 

 on Tancredia has a claim to priority, and the generic name which 

 I have chosen should be retained. More recently three addi- 

 tional species have been ascertained in our Great Oolite, and the 

 hinge- characters of a fine Inferior Oolite species have been deve- 

 loped : as the latter shell, from its superior size and the promi- 

 nence of its dentition, constitutes a remarkable example of the 

 genus, I propose to describe it in detail, premising that the same 

 species, in a greatly diminished form, was figured in the plate 

 which accompanied the memoir of 1850, under the name of 

 T. donacifonnis. The small figure there given represents the 

 usual size of specimens obtained in the shelly freestone of Leck- 

 hampton Hill ; the larger examples now to be described occur not 

 unfrequently in the bed called Gryphite grit, at Rodborough Hill, 

 near Stroud, a locality which has produced so many novel and 

 finely-preserved testacea. Upon comparing the hinge of the 

 new shell with that of T. extensa, which was figured in my me- 

 moir, the difference between them is found to be considerable, 

 and it requires a close scrutiny to perceive that the parts and 

 their arrangement are alike in both, modified by the more ad- 

 vanced growth of the larger shell, and still more so by the pecu- 

 liarities of the species. 



The dental characters of T. extensa have much less prominence ; 

 they project but little vertically, and are more extended longi- 

 tudinally. A similar difi^rence is observable between the species 

 which M. Buvignier has figured : his T. Broliensis in its hinge 

 approaches to that of our large shell ; but the hinge of his smaller 

 and more elongated species, Deshayesea, presents a near resem- 

 blance to that of our T. extensa ; the greater obliquity of the 

 cardinal tooth in the elongated species is strongly marked, more 

 especially in the left valve. The Rodborough examples of T. do- 

 naciformis may be regarded as representing the hinge-featm-es 

 in an exaggerated form, the result in some degree of greater age, 

 inasmuch as smaller shells from the same locality lose much of 



