INOCERAMUS. 



319 



intermediate between this type and those with rounded folds occur. It may 

 be convenient to adopt for this variety the name 7. Lamarchi var. Websteri. It 

 appears to occur mainly in the zone of Micraster cor-testudin avium. 



1. uiidalatus, Mantell (PI. LIII, fig. 3), resembles small forms of I. B rongniarti, 

 Sowerby, but the folds are much smaller, more numerous, and less conspicuous, 

 and the shell is thicker than usual. 



Fig. 77 '. — Inoceramxis Lamarchi var. Cuvieri, Sow. Upper Chalk (zone of Holaster planus), Swaffham, 



Norfolk. Norwich Museum. Left valve, x J. 



Some small forms (PI. LIII, figs. 4— G), found in the Middle Chalk and in 

 the /one of Holaster plana*, which may be named I. LamarcJci var. apicalis, 1 have 

 nearly equal valves, more prominent and more distinctly incurved umbones, with 

 the folds indistinct or absent, but these forms pass into others with distinct folds. 

 In some of these small forms the umbo is curved anteriorly (Plate LIII, fig. 4). 



1 An example of this from the Chalk Rock was figured in the ' Quart. Journ. Geol. Soc.,' vol. liii 

 (1897), p. 381, pi. xxvii, fig. 13. 



