APTYCHUS. 57 



Height, f- inch ; breadth of each valve, f inch. 



Found in the Upper Chalk of Norwich, by Mr. T. G. Bayfield, and in Fhnt Pebbles in 

 the Gravelj near Croydon. 



Of the Ammonites found in the Upper Chalk, the one of which the outhne of the 

 mouth most nearly resembles this Apiyclius is A. GoUevillensis (PL XXIV, fig. 15). I 

 have not seen this species of Ammonite from Norwich ; but as, besides being found in the 

 North of Ireland, it occurs in France, in the Upper Chalk of the department of the 

 Manche, it may be expected to occur also on our side of the Chaunel ; so that it is probable 

 that the Aptychus here described belongs to Ammonites GoUevillensis. 



Of the varieties of Aptychus cretaceus figured by Geinitz, one form {I. c., 1. 17, fig. 25 ^) 

 approaches our species, but does not admit of absolute identification with it. 



Aptychus Icenicus, Sharpe. Plate XXIV, fig. 7 a, b. 



A.bivalviSyOvalis ; valvis imbricatis : latere convexo rugis paucis, latisjonyitudinalibm, 

 inconspicuis, ornato : plica media parvd. 



Bivalve, very thin ; oval, with nearly straight sides : valves very convex, especially 

 towards the lower end : the convex side faintly marked by a few broad, longitudinal folds, 

 which are not parallel to one another, and which cross the imbrications : medial fold small 

 and straight : the concave side has not been seen. 



Height, I" inch ; breadth of each valve, 5 inch. 



Found in the Upper Chalk, near Norwich, by Mr. T. G. Bayfield. 



Ammonites Icenicus is the only species yet seen from the Upper Chalk which has its 

 opening correspondnig to the peculiar outline of this Aptychus, which has its sides nearly 

 straight, and its two extremities nearly equal ; and as both are found in the Upper Chalk, 

 near Norwich, there is every probability that they must be connected. 



AriTCHUs RUGOsus, Sharpe. Plate XXIV, figs. 8 a, b, and 9. 



[A. bivahis, truncato-oblongus ; valvis imbricatis^ latere convexo corrugatis, plicis dis- 

 tantibus, elevatis, tuberculatis, ayitice angulariter injlectis. 



Bivalve ; together oval or oblong, and notched at each end ; separate plates nearly 

 flat, thin, finely imbricated by fines of growth on the concave side, and ornamented with 

 elevated wi-inkles on the outer surface; ridges from \ line to 1 line apart, irregularly 

 tuberculated, sub-parallel with the outer margin, and bent back at a sharp angle at the 

 upper end ; slightly irregular and flexuous, and becoming obsolete near the suture. 



