18 MR. H. WOODS ON THE EVOLUTION OF [Feb. I912, 



The ' genera ' Endocostea Whitfield ^ and Haenleinia Biihm- have 

 almost certainly been derived from I. halticus and should, I think, 

 be included in the genus Inoceramus. 



I. lingua Goldf. (fig. 90, p. 17),^ from the zones of Marsuj)ites 

 testudinarins, Actinocamax quadratus, and Belemnitella mucronata, 

 also appears to have descended from the flat form of /. inconstans, 

 which it resembles closely. The principal differences seen in 

 /. lingua are the greater relative height of the shell, giving more 

 acute umbones, the rather less convex valves and consequently 

 smaller anterior area. In /. lingua the flat stage appears to have 

 continued throughout life. 



I. lohatus Goldf. (fig. 91, p. 17),* from the zones of Marsu^ntes 

 testudinarius and Actinocamax quadratus, is very closely allied to 

 /. lingua; but in it an angular ridge or carina between the umbo 

 and the postero- ventral extremity has been developed, and in front 

 of this is a sulcus : the ridge gives a definite line of separation to 

 the posterior ear, and the sulcus causes the ribs to become sinuous. 

 A further difference from /. lingua is generally seen in the more 

 distinct differentiation of the ribs into two sizes. 



/. cardissoides Goldf. (fig. 92, p. 17)," from the Upper Chalk 

 (probably zone of Actinocamax quadratus)^ is closely related to 

 /. lohatus ; but radial ribs have been developed, and the concentric 

 ribs have become stronger. 



J. tuherculatus Woods (fig. 93, p. 19),^ from the zone of Actino- 

 camax quadratus, possesses the main characters of J. lohatus and 

 /. cardissoides. It appears to have arisen from the former by the 

 development of radial ribs which, in combination with the concentrio 

 ribs, give a tuberculate type of ornamentation. 



I. undulatO'plicatus Rom. (fig. 94, p. 19),"^ from the Upper Chalk, 

 is of the same type as the flat forms of /. inconstans, especially in 

 its early stages where concentric ribs only are present ; but subse- 

 quently diverging radial ribs are developed. Athough no connecting- 

 forms have been found, it seems probable that this species has 

 descended either from /. inconstans or from some closely related form. 



1 'Prelim. Eep. Palseont. Black Hills' (Powell's Geol. & Geogr. Surv. 

 Bocky Mt. Eegion, 1877) p. 31 : and ' Palaont. Black Hills of Dakota ' (U.S. 

 Geol. & Geogr. Surv. Eocky Mt. Eegion. 1880) p. 402. See also A. d'Orbigny, 

 ' Pal. Fran9. : Terr. Cret.' vol. iii (1846) p. 515 & pi. ccccix ; H. E. Beyrich, 

 Zeitschr. Deutsch. Geol. Gesellsch. vol. iv (1852) p. 151 & pi. v; & J. Bohm, 

 Abhandl. d. k. Preuss. Geol. Lanciesanst. n. s. pt. ivi (1909) p. 48. 



2 J. Bohm, ihid. (1909) pp. 53-58 & pis. xiii-xiv. 



3 H. Woods, op. cit. text-fig. 56. 



4 Id. ihid. text-figs. 54 & 55. 

 » Id. ibid, text-figs. 57 & 58. 



" Id. ihid. pi. liv, fig. 8 & text-fig. 59. 

 '' Id. ibid. text-^ss.e>0& 61. 



