304 CRETACEOUS LAiMELLIBRANCHIA. 



Inocekamus UNDULATO-rncATiis, lujiiicr, 1852. Text-figs. 60, 01. 



1852. Inoceramus undulato-plicatus, F. llinner. KreidcliilJ. v. Texas, p. i>9, 



pi. vii, fig. 1. 

 1865. — DiGiTATUS, F. A. Ei'niier. Palaontographifa, vol. xiii, p. 196, 



pi. xxxii, fig. 6. 

 1873. — — F. Schmidt. Mem. Acad. Imp. Sci. de St. 



Pctersl)., ser. 7, vol. xix, no. 3, 



p. 25 (partim), pi. v, figs. 10, 11 ; 



pi. vi, fig. 1, 2, 4, 6, 7 ; pi. vii ; 



pi. viii, figs. 9 — 15. 



1877. — • UNDULATO-PLICATUS, C. Scltliiter. Paleeontographica, vol. 



xxiv, p. 270, pi. xxxviii, 

 fig. 1. 



1878. — — C. Barrois. Ann. Soe. gcol. du Nord, 



vol. V, p. 475. 

 1894. — DioiTATUs, A'. Jiiiiho. Palaeont. Abhaudl., vol. vi, p. 43, 



pi. viii, figs. 8—10. 

 1899. — ScHMiDTi, B. Michael. Jahrb. d. k. preuss. geol. Laudesanst. 



fiirl898, vol. xix, p. 162, figs. 1—4. 



Descyiptloii. — Shell ovate, much higher than long, very inequilateral ; the early 

 part of the shell of small or moderate convexity, the later part only slightly convex 

 or nearly flat. Hinge-line forming more than a right angle with the anterior 

 margin. Umbones terminal, small, curved anteriorl}'. 



Ornamentation consists of concentric and radial ribs ; the former are more 

 distinct on the early part of the shell, the latter on the later part. The radial ribs 

 curve outwards from a line between the umljo and the postero-ventral extremity ; 

 they have rounded summits, and arc separated by broad shallow interspaces ; a 

 tubercle or rounded elevation may l)e developed where the concentric ribs cross 

 the radial ribs. 



A[fiiii,fiet>. — This species is closely allied to J. Jiijitatns, Schliiter {nun 

 Sowerby) . 



The fact that in some specimens the early part of the shell is ornamented with 

 concentric folds only, and the radial ril)s appear on the later parts, suggests 

 that this species has been derived from one with concentric folds only, in a 

 manner similar to that in which 1. sulcatus has arisen from /. coiicentricus (see p. 

 2G8) ; the specimens at present available, however, do not enable us to trace the 

 origin of I. undulato-])licatiis, but it seems probable that it has descended from a 

 flat variety of I. inconstans. 



Forms from Vancouver Island with a similar type of ornamentation have been 



