288 



CRETACEOUS LAMELLIBRANCHIA. 



curvature of tlio I'ibs varies. In some specimens (often of large size) the shell 

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

 7. Lamarcld var. Wi-bsteri, Mant. (p. 818). Further work may show that it is 

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



Affinities. — This species is closely allied to /. hihiatns var. lafus, Sowerby;' 

 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 

 ai'e less jirominent and the posterior ear more distinct. 



.#■.-.-• \Vi9'.^3r ■ mr-.—Ja 



Fig. -t". — Inocevamus iticnnstans, sp. nov. Upper Chalk (zone of Actinocamax quadratiis), liii|^')iton. 

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



7. incon,<itan>i is distinguished from 1 .Lamarclci, Parkinson (p. 807), 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 

 tlie smaller difference in the size of the valves. 1. Guvien of Andert" appears to 

 l)e a flat form of /. inconstans. Another specimen figured by Andert'' is allied to 

 7. ineonstivutt, but its a.xis of growth is more ol)lique and its hinge longer than usual. 



1 Erratum ou p. ^84 (fig. 39) : for Tvoceramvn Jahiatus var. latug. Sow., read Inoceramns incon- 

 stayis, sp. uov. A specimen figured by Audert (' Inocerameu d. Kreiltitz-Zitfavier Sandsteingeb.,' 1911, 

 ]). 45, pi. i, fig. 5) as I. Cuvieri var. planus appears to be iuterinediate between I. lahuitita aud/. labiatus 

 var. latus. 



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



' Loc. cit., pi. i, fig. 2, pi. vii, fig. 8 (/. Cuvieri var. ^'/("(".s). 



