wHiTEAVEs.] FOSSILS OF TRIASSIC ROCKS OP BRITISH COLUMBIA. 129 



narrow on and near the beaks but which widens rapidly towards the 

 front margin, its maximum width being not much less than one-half the 

 greatest breadth of the whole valve. Umbo broad, curved and slightly 

 depressed, but projecting considerably above the general level of the 

 hinge line : beak incurved and slightly decurved : area concavely 

 arcuate, broadly triangular in outline and nearly three times as broad 

 as high : pseudo-deltidium rather narrowly triangular and apparently 

 a little higher than broad. Sarface marked with five well-defined, 

 angular, radiating plications on each side of th^ mesial sinus and with 

 one in the sinus. 



Dorsal valve also moderately convex, its me.-'ial fold elevated and 

 somewhat narrower than, but in other respects corresponding to, the 

 sinus in the opposite valve. Umbo narrower and very much less ele- 

 vated than that of the ventral valve, its beak lightly incurved. Surface 

 marked with two well-defined and angular radiating plications on the 

 mesial fold, and with four similar ones on each side. In addition to 

 the radiating folds, the surface of each valve is marked with numerous 

 and for the most part rather closely disposed lines of growth. 



Characters of the interior of the valves unknown. 



Dimensions of the only specimen collected : maximum length, 

 twenty-nine millimetres; greatest breadth, thirty-three mm. and a 

 half; maximum thickness through the closed valves, twenty-one mm. ; 

 greatest breadth of the mesial sinus of the ventral valve, fourteen mm. 



Liard Eiver, about twenty-five miles below Devil's Portage, E. G. 

 McConnell, August, 1887 : one perfect but somewhat distorted and 

 abnormally developed specimen. 



On the right-hand side the two radiating plications next to the outer 

 boundary of the mesial sinus in the ventral valve and the one next to 

 the fold in the dorsal, bifurcate distinctly at about their midlength, 

 whereas on the left-hand side all the plications are clearly simple and 

 undivided throughout their entire length. 



Terebratula Humboldtensis, Gabb. 



Terehraivla Humholdtenm, Gabb. 1864. Geol. Surv. C'al., Palceont., vol. I., p. 34, 



pi, 6, figs. 35 and 35 a, b- 

 Hall and Whitfield (as of Gabb). 1877. U.S. Geol. 

 Expl. Fortieth Parallel, vol. IV., p. 282, pi. 6, figs. 

 22-24. 



McDonald's Eiver, on Nicola Lake, Dr. G. M. Dawson, 1887, as 

 already recorded on page 171 B of the " Eeport of Progress of the 

 Geological Survey of Canada for 1877-78-" 



