298 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



Lake "VViixnipegosis, on the north-west side, at Devils Point (a cast of 

 the interio]- nf both valves) ; on the south-west side of Dawson Bay, two 

 miles west of Salt Point (one specimen with the test preserved), and on 

 the west side of Dawson Bay, at the lirst small point north of the mouth 

 of the Red I)ecr River (nine casts uf the interior of the partly open or 

 displaced valves) ; J. B. Tyrrell and D. B. Dowling, 1889. 



Some of these specimens are more obliquely truncated posteriorly and 

 more pointed at the base, than is the case with the original of fig. 1 '2. 

 Such indi\iduals bear a rather close resemblance, both in lateral outline 

 and in size, to some forms of the Mnz/ii'/hi. pijijuuHi of Conrad, as figui'ed 

 by Hall*, but in that species the \'alves af(i much more convex propor- 

 tionately, and not at all angulated on tin; posterior umbonal slopes. 



(S.) Spatiiella subelliptica. (N. Sp.) 



Plate .3S, fig. ]2. 



Shell rather small, narrowly subelliptica], rather less than twice as long 

 as high, but a little higher behind tlie midlength than in fiont of it, and 

 xevy ine(|uilateral. \^alves usually tumid and strimgly convex in the um- 

 Ijonal region, but narrowing rather rapidly into the ventral and posteiior 

 margins : anterior side narrow, very short and rounding abi'uptly into the 

 ventral mai'gin : posterior side broader and much longer than the ante- 

 rior, its extremity narrowly rounded ; cardinal line occupying about one 

 half of the entii-e length, nearly straight, but very slightly ascending 

 posteriorly: ventral margin nearly straight, slightly convex and almost 

 parallel with the cLji'sal margin : beaks small, depressed, incurved, ante- 

 rior a)]d very neaily but not quite terminal. 



Sui-face marked with concenti-ic strite anrl rais('d lines of growth, which 

 latter are most prominent posteriorly. Hinge dentition and muscular 

 impressions unknown. 



Maximum length of the specimen figured, twenty-five millimetre's and 

 a half ; greatest height of the same, foui'tec'n mm. 



Pentamerus Point, Lake Manitoba, J. B. Tyrrell and J. F. Whiteaves, 

 1888 : ix nearly perfect specimen, which, however, is much less convex in 

 the umbonal region than usual. Western sh(jre of Dawson Bay, Lake 

 AVinnipeg(wis, on the second small point north (jf the mouth of the Red 

 r)eei' Ri\'ei', D. B. Dowling, l.S.SO : eight specimens, two of which are 

 neaiiy perfect, and upon which the foregoing deseiiption is based. A 

 Ybx-y imperfect specimen from the noi-th side of South j\[anitou Island, in 

 Lake Wimiipegosis, and an equally impeifect one from an exjiosure a 

 mile a])0\e the Lower Salt Spiing on the Red Deer River, both collected 

 by 31r. Tyrrell, in 1889, are probably i-eferable to the pres(.'nt species. 



Pal. St. N. York, vol. V, pt. 1, Lamellibr., 2, \,. oH, i>l. l.\.\vi, figs. '.)-20. 



