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SUPPLEMENT TO THE BRITISH 



Length of a very large example eight lines, by twelve in breadth, but the shell rarely 

 exceeds ten lines in width, and is usually even smaller. 



06s. This fine species, the largest of the genus hitherto discovered in the Liassic 

 deposits, is at once distinguishable from all the others from that formation by its shape 

 and dimensions. It is exceedingly abundant, and in a perfect state of preservation, in 

 the highest bed of the Upper Lias, a sandy clay, full of fragments of Encrinites, at May 

 in Normandy, where it was first discovered by Mr. Perrier. It was subsequently col- 

 lected in great numbers in the same locality by Messrs. Deslongchamps, father and son, 

 and by myself, and was admirably described and figured by Mr. Eugene Deslongchamps 

 in his excellent memoir on the Genera Lepta-na and Thecidea from the Jurassic Formation 

 of Calvados. In 1860 a small single dorsal valve was found by Mr. C. Moore in the 

 Upper Lias of Ilminster, where the species appears to be rare. Mr. R. Tate refers this 

 species to both the Middle Lias or Zone of Am. margaritatus and the Upper Lias with 

 Am. bifrons (' Geol. Mag.,' vol. vi, p. 554). 



27. Lept,ena Bouchardii, E. Best. Dav., Ool. Mon., p. 19, PI. 1, fig. 22. 



Lept.ena Bouchardii, E. Deslongchamps. Memoires de la Soc. Linn, de Normandie, 



vol. ix, pi. xi, fig. 5, 1853. 



Mr. Deslongchamps observes that this pretty little species is easily distinguishable 

 rrom Leptcena liasiana by its more elegant shape, uniform curve, and smaller dimensions, 

 the beak also never being perforated. A single specimen showed lateral auricular 

 expansions, but these, being very fragile, were easily broken during the life of the animal 

 or in the process of fossilisation. It occurs but rarely in the Lias of Fontaine-Etoupe- 

 Eour, near Caen, in Normandy. In addition to what we have stated with respect to this 

 species at p. 19 of our Oolitic and Liassic Monograph, we may add that Mr. R. Tate 

 quotes the fossil from the Middle Lias zones of Am. capricornus and Am. margaritatus, 

 and from the Upper Lias zone of Am. bifrons. 



28. Leptjena rostrata, E. Best. Sup., PI. X, fig. 30, 30 a, b. 



Lept^na rostrata, E. Desl. Annuaire de l'lnstitut des Provinces for 1855, p. 52, 



pi. — , figs. 17, 18, 1855. 



Spec. Char. Shell minute, marginate, pear-shaped, or longer than wide : widest 

 about the middle and broadly rounded anteriorly, tapering posteriorly to an almost 



