224 CONTRIBnTIONS TO CANADIAN PALAEONTOLOGY. 



also Pembina Eiver, four mile.-; above it:< mouth, E. G. McConnell, 

 1890. 



S. inutilis would seem to be nothing more than a mere variety of S. 

 subatfenuata, in which the hinge area of the ventral valve is propor- 

 tionately larger and higher, and the cardinal extremities of both valves 

 not nearly so much produced. 



Spirifeea tdllia, Hall. Var. 



Plate 32, figs. ], la, b. 

 Spirifera tullia, Hall. 1867. Pal. St. N. Y., vol. IV, p. 21S, pi. xxxv, figs. 1-9. 



Shell small, transverselj' subelliptical or somielliptical, a little 

 broader than long and broadest just behind the midlength: cardinal 

 angles more or less rounded, lateral margins rounding regularly into 

 the front, which is shallowly concave at the termination of the mesial 

 fold and sinus. Ventral valve much more convex than the dorsal, most 

 prominent in the umbonal region, with the sides curving regularly to 

 the margin, but dejiressed in the conti'C, its mesial sinus well defined, 

 rounded, very narrow on the beak and umlio, but widening rather 

 raj)idly toward the front, where its width slightly exceeds one third of 

 the greatest breadth of the valve: beak small, not very prominent, its 

 apex only being slightlj' incui'ved, but not so much so as to cover or 

 overarch any part of the fissure: area moderately high and slightly 

 concave: fissure triangular, higher than wide, with an impressed line 

 or uai'row linear groove on each side. .Dorsal valve veiy gently con- 

 vox, its mesial fold rounded and not much elevated, sometimes with a 

 faint narrow depression in the centre, its hinge line nearly sti'aight 

 and its beak minute and projecting vcrj' little abuve the cardinal 

 mai-gin. 



On each side of the mesial f )ld and sinus there are from seven to 

 nine rounded hut somewhat flattened and simple radiating libs or pli- 

 cations, but there are none on the fold oi' sinus. In addition to 

 the ribs, the whole surface when examined under a lens is seen to be 

 marked with exceedingly numerous, close-set and minute, but con- 

 tinuous, radiating raised lines, which are crossed by equally minute and 

 nearly as densely crowded concenti-ic raised lines, in .such a waj' as to 

 produce an exquisitely fine netwoi'k, which is subgranuloee at the 

 points of intersection. The i-adiating raised lines are not alwaj's 

 exactly parallel to the ribs, and the concentric ones are regularly 

 arched where they cross over the ribs, fold or sinus. 



