288 



CRETACEOUS LAMELLIBRANCHIA. 



curvature of the ribs varies. In some specimens (often of large size) the shell 

 is thinner than usual and has sharp and ridge-like folds similar to those of 

 I. Lamarcki var. Websteri, Mant. (p. 318). Further work may show that it is 

 desirable to give names to some of the varieties of I. inconstans. 



Affinities. — This species is closely allied to I. labiatus var. latus, Sowerby; 1 

 but the hinge is relatively longer and the height of the shell less, the anterior 

 flattened area is larger, the later part of the shell is more convex, the umbones 

 are less prominent and the posterior ear more distinct. 



"^ 



Fig. 47. — Inoceramus inconstans, sp. nov. Upper Chalk (zone of Actinocamax quadratus), Brighton. 

 Brighton Museum, No. 336. Right valve and anterior view. Natural size. 



I. inconstans is distinguished from I . LamarcM, Parkinson (p. 307), by the 

 relatively longer hinge-line, the more unsymmetrical curvature of the folds, the 

 flattened form of the early part of the shell, the less prominent umbones, and 

 the smaller difference in the size of the valves. 1. Guvieri of Andert 2 appears to 

 be a flat form of I. inconstans. Another specimen figured by Andert 3 is allied to 

 I. inconstans, but its axis of growth is more oblique and its hinge longer than usual. 



1 Erratum on p. 284 (fig. 39) : for Inoceramus labiatus var. latus, Sow., read Inoceramus incon- 

 stans, sp. uov. A specimen figured by Andert (' Inoceramen d. Kreibitz-Zittauer Sandsteingeb.,' 1911, 

 p. 45, pi. i, fig. 5) as I. Citvieri var. planus appears to be intermediate between J. labiatus and/, labiatus 

 var. latus. 



~ Loc. cit., pi. ii, fig. 2. 



3 Loc. cit., pi. i, fig. 2, pi. vii, fig. 8 (/. Guvieri var. planus). 



