Mr. S. P. Pratt on the Geology of Bayonne. 55 



(2.) Elasmodus {eKuayta lamina, dlovs dens). 



Two maxillary and two intermaxillary plates in the upper jaw ? 



Two maxillary plates in the lower jaw ; lower maxillary thick and 

 strong ; tubercle single, composed of a dental substance resembling 

 in structure a tritor of Psammodus ; in advance of the tubercle the 

 tooth is composed of several series of laminae, arranged in juxta- 

 position and inclined downwards and outwards ; behind the tubercle 

 the dental edge is notched, in consequence of a columnar structure 

 pervading this region of the tooth. The outer surface is enveloped 

 by a coat of dentine. 



A single specimen in the Hunterian collection affords the type of 

 a third genus. 



(3.) Psaliodus (xpaWs forfex, and odovs dens). 



Upper jaw ? Two maxillary plates in the lower jaw. Lower max- 

 illary like Chimcera, but without a triturating tubercle ; structure 

 homogeneous ; outer surface reticulated. Sp. Psaliodus compressus, 

 Egerton. It is supposed to be From the London clay. 



" On the Geology of the Neighbourhood of Bayonne." By Samuel 

 Peace Pratt, Esq., F.R.S. 



After noticing the published descriptions of the geological struc- 

 ture of the neighbourhood of Bayonne, by M. Dufrenoy, M. le Conte 

 D'Archiac, and M. de Colligno of Bordeaux, the author proceeds 

 to detail the result of his own observations in that locality in 1842. 



Bayonne, situated at the junction of the rivers Adour and Nive, 

 about four miles from the coast, is nearly surrounded by low hills of 

 sand and gravel, those on the north side of the river being appa- 

 rently a prolongation of the beds of pudding-stone and gravel which 

 form a ridge extending from Tarbes to Pau, in a direction nearly 

 east and west to the coast. The gravel and alluvium on the south 

 differs in mineralogical character, and forms a thin coating to a suc- 

 cession of deposits of sand, clay and impure limestone which rise to 

 the south-west towards the coast. The sandy limestone, which is 

 composed almost entirely of Lenticulites complanatus and Nummulites 

 Biarritzana {N. elegans?), with a few fragments of shells, chiefly 

 Pectens, forms for a short distance the north bank of the river 

 Nive, rising at an angle of 20° or 30°. It is for the most part 

 covered up by beds of sand and variously coloured clays, resembling 

 the plastic clay. The gravel is very variable in thickness and con- 

 tains no flint, but is chiefly composed of rounded and irregular 

 masses of sandstone very like the Bagshot sandstone. The country 

 in this direction has been much disturbed. 



About four miles in a south -west direction from Bayonne is the vil- 



* Chinijcra Greenovii, Jgassiz. f Chimsera Hunteri, Owen. 



