58 FOSSIL MOLLUSCA OF THE CHALK. 



Height of largest specimen (fig. 9), 2^ inches; breadth of single valve, 11 lines. Small 

 pair (fig. 8), height, 1^ inch; breadth, 1 inch. 



From the Upper Chalk of Norwich, in the collections of Mr. John King and Mr. 

 T. G. Bayfield.] 



Aptychus peramplus, Sharpe. Plate XXIV, fig. 10 a, b. 



A. bivalvis ; truncato-ovatus ? valvis imbricatis, latere convexo corrugatis, latere concavo 

 mbtiliter concert trice lineatis : plica media elevatd. 



Bivalve ; truncato-ovate ? valves imbricated, thin near the medial fold, thicker towards 

 the edge ; convex side corrugated, the corrugations covered with irregular and unequal 

 tubercles ; concave side marked by fine concentric lines, indicating the edges of the closely 

 set imbrications : medial fold large. 



From the Chalk, near Norwich, in the collection of Mr. Bayfield. 



I have only one fragment of this Aptychus, \\ inch in breadth, and can offer but an 

 imperfect description of it : the convex side is concealed in the specimen, and the direc- 

 tion of the corrugations cannot be seen. It is with great hesitation that I propose to 

 connect it with Ammonites peramplus. 



[This specimen was described by Mr. Bayfield in 1851 ('Annals and Magazine of 

 Natural History/ 2d series, vol. viii, p. 23G), being the first instance on record of the 

 occurrence of Trigonellites in the English Chalk.] 



Since the preceding descriptions of the species of Aptychus were in type, a memoir* 

 has appeared on the Cretaceous Fossils of Meudon, France, by M. Ed. Hebert, in which 

 three species of Aptychus are described ; A. obtusus, crassus, and insignis, the last form 

 being closely allied to, if not identical with, A. rugosus, above noticed. 



* Mem. Soc. Geol. de la France, vol. v, p. 367, pi. 28. 



