288 



the head of Shoal River, Manitoba, collected by Mr. Tyrrell in 1889. 

 This valve is associated with several characteristic specimens of Siropheo- 

 donta acanthoptera. 



The specimens from Ami Island and the Saskatchewan upon which 

 this species is based, are those that were referred to Pterinea aviculoidea, 

 with a query, in the provisional lists of fossils that accompany Mr. 

 Tyrrell's report. But it has since been apparent that they differ materi- 

 ally from the Wisconsin specimens of that species, as figured by Whitfield, 

 (1) in their different marginal outline, (2) in their more prominent 

 umbones, and (3) in their proportionately larger anterior wing. 



IlIONIA (?) PARVULA. (N. Sp.) 



Plate 28, figs. 6, 7 and 8. 



Shell small, compressed, narrowly and ovately subelliptical, nearly twice 

 as long as high. Anterior side narrowly rounded ; posterior side more 

 pointed but not much longer than the anterior ; beak small, low, incurved, 

 and placed not far from the midlength. 



Surface closely and concentrically ribbed. 



Hinge dentition and muscular impressions unknown. 



Ami Island, one left valve ; and Long Point, two right valves ; all of 

 which are figured of the natural size. 



This little shell may prove to be only a small form, or perhaps a mere 

 local variety of the Ilionia (?) costulata, from the Guelph formation of 

 Ontario, which is described and figured in the first part of this volume. I. 

 parvula, however, seems to be uniformly smaller than I. costulata, and the 

 beak of the former is placed nearer the midlength. Both of these shells 

 are only provisionally referred to Ilionia. They are probably indicative 

 of a new generic type, which there is not yet sufficient material to define 

 satisfactorily. 



Gasteropoda. 



The gasteropoda in the collections made by Mr. Tyrrell on the north- 

 eastern side of Lake Winnipegosis are imperfect and indeterminable casts 

 of the interior, or moulds of the exterior, of the shell of two species of 

 Murchisonia, and of one species each of Pleurotomaria and Straparollua. 



CRUSTACEA. 



Ostracoda. 



Isochilina gbandis, var. latimaeginata, Jones. 



Isor.hilina grandis, var. latinuirgwata, Jones. .1891. Contr. Canad. MicroPalaeont., pt. 



Ill, p. 78, pi. 10, figs. 1, », b, c ; 2, a, b, o ; 

 and 3, 4. 



