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, IJ inch; breadth, 1 inch. 



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

 T. G. Bayfield.] 



Aptychus peramplus, S/iarpe. Plate XXI V^ fig. 10 a, I/. 



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

 subtiliter concentrice 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 Aptyclms, 1^ 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 Ammo7iites peramplus. 



[This specimen was described by Mr. Bayfield in 1S51 ('Annals and Magazine of 

 Natural History,' 2d series, vol. viii, p. 236), 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. rugofms, above noticed. 



* Mem. Soc. Geol. de la France, vol. v, p. '6i57, pi. 28. 



