272 



CRETACEOUS LAMELLIBRANCHIA. 



dicular to the plane of the valves; height greater than length. Hinge-line equal 

 to about two-thirds of the height of the shell. Ventral margin very convex; 

 posterior margin forming an obtuse angle with the hinge-line. Umbones terminal, 

 curved inwards and forwards, the left umbo larger and more prominent than the 

 right. Surface smooth, except for growth-rings. 



Affinities. — /. iciniis resembles I. conceutricitf;, but the left umbo is less 



Pig. 31. — Inoceramus tenuis, Mantell. Chalk Marl, Hamsey. The type, No. 5890, British Museum (Nat. 

 Hist.). The specimen is somewhat compressed from front to back. Left valve .and anterior view of both 

 valves. Eight valve shown in the next figure. 



prominent, the length of the shell is relatively greater, and the concentric rings 

 are less prominent. 



The fragmentary specimens described by Seeley as renm li'ssa appear to belong 

 to this species.^ 



Types. — In the British Museum (No. 5800) from the Chalk Marl of Hamsey. 

 A fragment, from the Red Limestone of Hunstanton, which appears to be one of 



^ The form from the Red Limestone of Hunstanton which was named Penia transversa by Seeley 

 is at present known only by an imperfect left, valve. It is perhaps allied to I. tenuis, but is remark- 

 able in being much longer than high. The type is in the Sedgwick Museum, Cambridge. Seeley, 

 'Ann. Mag. Nat. Hist.,' ser. 3, vol. xvii (1*1^66), p. 179. 



