286 



CRETACEOUS LAMELTJURAXCII lA. 



small part (Figs. 4:5, 48, 4'.») l)ut in others a large part (Plate LI, fig. 2, Text-figs. 

 45, 4(5) of the eiitii'(> shell.' Also the passage IVom one stage to tlie other is 

 sometimes gradual, so that the section ol" the shell t\)i'nis a fairly miiform eui-ve 

 (Fig. 48), but generally tlie change is abrupt, so that the later part of the valve is 



Fifi. 42. — Inocei-amus imuustans, sp. iiov. The orisjinal of I iioceramus sp.. Manti-ll, ' Foss. S. Downs,' p. 217, 

 pi. xxvii, h'r. y. Ujjpor Chalk, Lowes. Britisli Musoum, No. -ilO-'). Left valve and posterior view. 

 Natural size. 



>_>*'' 



Fia. 43. — Inoceramus incoHslttns, sp. nov. Zone of Holaster planus, Swall'hain, Norfolk. Norwirli Museum. 

 Left valve, and posterior and dorsal views of the same. Natural size. 



bent at an angle with the earlier part (Figs, l-^, I-!). The length of the hinge-line 

 in proportion to the height ot" the shell shows some variation and conse(piently the 



' Tlio larger spcciiucu of I. hifii:i, Sowcfliy (' Mill. Coueli.,' vul. vi, pi. dlxxxii. ujjper figure), 

 ■which eanuot uuw be foiuid, is ja-oliulilv an example of this. 



