WHITEAVES J DEVONIAN FOSSILS OF MANITOBA, ETC. 331 



(S.) Platyceras (Orthonyciiia) pahvulum. (N. 8p.) 



Plate 43, figs. 9, 10 and 11. 



Shell very small for the genus, nearly straight and somewhat conical, 

 but compressed at the sides, unsymmetrical and rather irregular in shape, 

 the posterior doi'sal slope being usually more convex than the anterior, 

 height varying in different specimens from a little greater to rather more 

 than one-thii'd greater than the maximum diameter at the base : apex 

 obtusely pointed, almost erect but with a slight fcjrward inclination : 

 aperture narrowly subelliptical, nearly twice as long as high, lip slightly 

 irregular in outline, but always with a deep concave sinus on each side, 

 and produced convexly downward and a little outward in front and 

 behind. 



Surface markings consisting apparently of concentric lines of growth, 

 which run parallel to the outer lip. Muscular impressions unknown. 



Dimensions of the largest specimen collected : maximum height, twelve 

 millimetres : greatest length at the base, eight mm. ; breadth of aperture, 

 five mm. 



Dawson Bay, Lake Winnipegosis, on a small island north of Whiteaves 

 Point (one specimen, the original of fig. 11), and on another south-west of 

 that point (two specimens, represented by tigs. 9 and 10) ; J. B. Tyrrell, 

 1889. 



The few specimens collected are all mere casts of the interior of the 

 shell. These appear to represent a small and aberrant or abnormal and 

 previously undescribed species of the subgenus OrtJtoniji'hin, most closely 

 related to the Platyceras (Orthonychia) conoideuiii- of Goldfuss, from the 

 Stringocephalus limestone of the Eifel and Nassau, as figured by Freeh,* 



(S.) Plattostoma tumidum. (N. Sp.) 



Plate 43, fig. 12. 



Shell subglobose or broadly subovate, imperforate, spire small and very 

 short, raised verj' little or not at all above the highest level of the outer 

 volution. Volutions apparently about three (though the apex is imper- 

 fect in all the specimens collected) rounded, increasing very rapidly in 

 size and closely embracing, by far the greater portion of the earlier ones 

 being covered by the overlapping of those which succeed them : outer 

 volution regularly convex, very ventricose and widely spreading, especi- 

 ally at and near the aperture, a little depressed below the suture, broader 



* Zeitschr. der Deutsch. geolog. Gesellschaft, 1891, vol. XLIII, p. 678, pi. xliv, 

 figs. 6, 6a.-c. 



