INOCERAMUS. 



31 



74, 79). In some varieties the area forms a sharp edge with the sides of the 

 valve (Fig. 81), in others the boundary is curved and the limit of the area is 

 indistinct (Fig. 85). 



In the type of I. Lamarcki, Parkinson (Fig. 63), the shell is inflated, and the 

 posterior ear well developed and sharply limited. In forms like I. Brongniarti 

 Sowerby (Fig. 70, PI. LII, fig. 4), the posterior ear is also well developed, but 



369 



Fig. 75. — Inoceramtts Lamarcki var. Cuvieri, Sow. Upper Chalk, Southerarn, Lewes. Brighton Museum, 

 No. 340. Portion of a left valve resembling the type of I. latus, Mant. x f . 



not so sharply limited as in the type of I. Lamarcki. Mantell's L. Lamarcki 

 (Fig. 66) is similar to J. Brongniarti, Sowerby, but has less prominent folds and 

 a more concave anterior border. I. Brongniarti, Sowerby, passes gTadually into 

 forms like the type of L. Brongniarti, Mantell (Fig. 68), in which the limit of the 

 posterior ear is somewhat indistinct. Other varieties possess similar strong folds 

 but have less convex 1 valves (as in I. Cuvieri, Mantell, Figs. 69, 84), and these 



1 In some cases the smaller convexity may be due to pressure which gradually changed the 

 shape of tbe shell. When no fractures are seen, flattening appears to be indicated in some cases by 

 the growth-lines cutting the folds obliquely. 



42 



