CAMBRO-SILURIAN MICRO-PALEONTOLOGY. 4^ 



LePERDITIA 8UBCYLINDRICA. (N. Sp.) 

 PI. IX., figs. 4-46. 



Yaives rather strongly convex, elongate ovate, the posterior half ^ 

 little the highest. End view sub-elliptical ; edge view acutely elliptical. 

 Anterior and posterior ends strongly and nearly equally rounded. 

 Dorsal line straight, the ventral nearly so. Right valve larger than 

 the left, and distinctly overlapping it along the ventral margin. Yaives 

 evenly convex; surface smooth, apparently without markings of any 

 kind. 



The only specimen seen gave the following measurements : greatest 

 length, 2.1 mm. ; greatest height (from posterior extremity of hinge 

 line to ventral edge), one millimetre , height from anterior end of 

 hinge line to ventral edge, 0.9 mm.; greatest convexity of the twa 

 valves in conjunction, 0.Y8 mm. 



Stony Mountain, Manitoba : one specimen. 



This species belongs to the group of " smooth Leperditia^." Its small 

 size will distinguish it from most of the lower palaeozoic forms, i. 

 faba, Hall, from the Niagara group of Indiana, is closely related to it, 

 but differs in its form, being comparatively shorter and with more 

 curved dorsal and ventral mai'gins. 



Aparchites minutissimus, Hall. 



Leperditici {hochiUna) minutissima. Hall, 1871. Desc. New Species of Foss. from 



the Hudson River Gr., etc , p. 7. 



Hall. 1872, 24th Rep't. State Cab., p. 231, 

 pi. 8, fig. 13. 



Hall and Whitfield. 1875. Pal. Ohio, vol. 2, 

 p. 102, pi. 4, fig. 4. 



A single valve from Stony Mountain is referred to this species, 

 specimens of which are not uncommon at several horizons in the 

 Hudson River or Cincinnati group of Ohio, Indiana, and Kentucky. 

 A variety or very closelv related species occurs in the Trenton shales 

 of Minnesota. 



The relations of this species are somewhat doubtful, still I believe we 

 may assert with confidence that it is neither a Leperditia nor an 

 Isochilina. It most probably belongs to the group of " nonsulcate 

 Primitive", and, as Prof. T. Rupert Jones has just established the genus 

 Aparchites for their reception, we cannot do better than place the 

 species in it. 



The convexity of the valves varies, the surface In some individuals 

 being almost evenly convex, while in others it rises into an obtuselj^ 

 pointed subcentral prominence. 



Stony Mountain, Manitoba, R. W. Ells, 1875. 



