130 CONTRIBUTIONS TO CANADIAN PALiEONTOLOGY. 



Tekebratijla Liardensi.s. (N. Sp.) 

 Plate 17, figs. 2, 2 a, 2 b and 2 c. 



Shell rather below the medium size, varying in outline from some- 

 what narrowly ovate to almost circular, but always a little longer than 

 broad, moderately convex, the thickness through the closed valves 

 varying from a little less to slightly more than one-half the maximum 

 length, the broad sjoecimens being proportionately flatter than the 

 narrow ones. 



Ventral valve longer and more convex than the dorsal, its umbo 

 somewhat elevated but obtuse and distinctly recurved at its apex, which 

 latter is obliquely truncated in such a way that the produced inner 

 margin of the foramen overhangs and partially ovei-laps the small and 

 sunken deltidium. Foramen complete but apparently lightly chan- 

 nelled and rather spout-like in front, nearly circular in outline but a 

 little longer than wide. Front margin with two low, narrow, rounded 

 folds, which are sepai-ated by a shallow and equally narrow mesial 

 sinus, and which gradually become obsolete and disappear before 

 reaching the midlength. On the outer side of each of these folds there 

 is a correspondingly shallow but somewhat broader depression. 



Dorsal valve very gently convex, its umbonal region obliquely de- 

 pressed and its beak small and scarcely projecting above the highest 

 level of the hinge margin. Front margin with one central fold and 

 two lateral folds, which are low, rounded and soparaled by two shallow 

 depressions which do not extend quite as far back as those on the 

 ventral valve do. When examined with a lens, a faintly impressed 

 line, which probably indicates the existence of a raised mesial septum 

 within, may be seen to extend longitudinally from the umbo nearly 

 halfway to the front margin, along the centre of the exterior of the 

 valve. 



Surface nearly smooth and marked only with a few rather distant 

 lines of growth. Characters of the interior of the valve unknown. 



Dimensions of one of the largest specimens of the nai-row variety: 

 maximum length, nineteen millimetres; gi'eatest breadth, fourteen 

 mm. ; maximum thickness, ten mm. In the lai-gest sjjecimen collected 

 of the broad variety, the corresponding measui'cments are: length, 

 nineteen millimetres ; breadth, seventeen mm.; thiclcness, nine mm. 



Liard Eiver, about twenty-five miles below Devil's Portage, also 

 about thirty miles below the same portage, R. G. McConnell, 1887. At 

 the locality first mentioned, a small piece of limestone was obtained, 

 containing five specimens of this species in situ; while at the second 



