52 FOSSIL MOLLUSCA OF THE CHALK. 



laleraliter aiigulato, anfradibus compressis, sub-quadrilateralihus, ultimo tVV; aperturd 

 oblongd, antice truncatd." — D'Orhigni/, 'Terr. Cret.,' t. i, p. 324. 



The species thus described by M. D'Orbigii}', in 1840, was said to have been dis- 

 covered by M. Enieric in the " Craie Chloritces " at Vergons, Basses-Alpes ; but in a 

 later work, the ' Prodrome de Paleontologie,' t. ii, p. 98, it is referred to the " Neocomien 

 superieur ou Urgonien." 



The specimen figured in Plate XXHI, fig. 6, was obtained by Mr. Sharpe from the 

 Grey Chalk at Ventnor, in the Isle of Wight, and named by him " Feraudianus ;" but as 

 no memorandum exists to support this identification, it might possibly have been changed, 

 as it rests upon a single, crushed, and immature specimen.] 



44. Ammonites Bravaisianus, D'Orb. Plate XXHI, figs, la, b, 8, and 9. 



Ammonites Bra VAisiANUS, TfOrhigny. Paleontologie Frangaise, Terrains Cretaces, t. 91, 



figs. 3 and 4. 



A. testd compressd, carinatd, costatd : costis incequalibiis, simplicibus vel bifurcatis, 

 dorsum versus bituberculatis, interriiptis : dorso carinato ; carind elevatd, acuid : umbilico 

 magno : aperturd ohlongd. 



Shell discoidal, with few depressed whorls, which are ornamented by about thirty 

 transverse, slightly flexuous ribs : back keeled : the ribs are unequal, either simple and 

 alternately long and short, or occasionally branching in pairs from the edge of the 

 umbilicus ; each rib terminates at the side of the back, where it is ornamented with two 

 smaller tubercles : keel distinct, sharp, and elevated : umbilicus large, allowing two thirds 

 of the inner whorls to be seen : aperture oblong. 



Diameter, 1 inch ; height of last whorl, J inch ; width of aperture, \ inch. 



Found in a hard bed of the Middle Chalk, near Dover. In France it has been found 

 in the Upper Green Sand of the department of Vaucluse. 



This pretty little Ammonite has some resemblance to A. v avians, from which it is at 

 once distinguished by the pair of tubercles at the termination of each rib. Moreover, its 

 ribs are simpler than in that species, and never fork on the middle of the side of the whorl. 

 As yet A. Bravaisianus has only been found in this country in one bed of rather hard 

 Chalk, which occurs near the bottom of the Chalk with Flints, and contains A. peramplus, 

 Scaphites, and several other species of MoUusca hitherto undescribed, and only known in 

 that bed. 



