280 CRETACEOUS LAMELLIBRANCHIA. 



part flattened or concave, and more or less nearly perpendicular to the plane of 

 the valves. Ventral margm very convex ; posterior margin moderately convex. 

 Umbones terminal, incurved. Hinge-line nearly at right angles to the anterior 

 margin. Ornamentation consists of numerous strong, somewhat irregular concen- 

 tric ribs, separated by concave interspaces. The curvature of the ribs is 

 unsymmetrical, and the ribs become less distinct on the antero-dorsal and postero- 

 dorsal parts of the valves. 



Affinities. — This species shows some resemblance to I. anglicus, but possesses 

 more numerous ribs, and also differs in the anterior part of the shell being flat or 



Fig. 36. — Inoreramus pirtus, Sow. Chalk Marl, Guildford. British Museum No. 43272. The Type. 



Natural size. 



concave. The type and some other specimens {e. g. No. 73339, British Museum) 

 show traces of the original colouring of the shell. An example of this species 

 was figured by Grueranger as /. anguJatus, d'Orbigny,^ but appears to be quite 

 distinct from that form. 



Tij-pe. — From the Chalk Marl of Guildford, in the British Museum (Natural 

 History). 



Distribution. — Lower Chalk (zone of Rolaster suhglobosus) of Beachy Head, 

 Burham, Rochester, and the Gog-ma-gogs, near Cambridge. Chalk Marl of 

 Burham and Guildford. 



1 ' Pal. Frau?. Terr. Cret.,' vol. iii (1846), p. 515, pi. ccccviii, figs. 3, 4. In the text the spelling 

 is angnlosus. 



