280 



CRETACEOUS LAMELLIBRANCHIA. 



part flattened or concave, and more or less neai-lj perpendicular to the plane of 

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

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

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

 tric ribs, separated l)y concave interspaces. Tlie curvatui-e of the ril)s is 

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

 dorsal parts of the valves. 



Affinities. — This species shows some i-esemblance to I. amjlit-us, but possesses 

 moi'e numerous ribs, and also differs in the anterior part of the shell being flat or 



Fio. 3(). — Inoreramus juXiis, Sow. Clialk Marl, (iuiklfoid. liritish Musmim No. 4'.i'21'2. Tlic Typo. 



Natural size. 



concave. The tyi)e and some other specimens (e. tj. No. 73339, British Museum) 

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

 was figured by Gueranger as /. ancjulatus, d'Orbigny,' but appears to be quite 

 distinct fi'oin that form. 



Type. — From the Cluilk Marl of Guildford, in the British Museum (Natural 

 History). 



Dixfrihiifion. — LoAver Clialk (zone of JTohtstor siibriJuhosHs) of Beachy Head, 

 Burham, Kochester, and the Cog-ina-gogs, near Cambridge. Chalk Marl of 

 Burham and Guildford. 



' ' Pal. Fiau^. Terr. Crct.,' vol. iii (1816), j). ill.S, \A. ccccviii, figs. 3, -i. lu the text the spelliug 

 is ancjulosus. 



