352 THE PALEONTOLOGY OF MIls'NESOTA. 
[Lingula canadensis. 
more obtuse. The ventral valve in L. ioivensis and L. heltrami is also less convex 
than the dorsal, while in L. cincinnatiensis and L. quadrata Eichwald (non Hall) they 
are equally deep, but the latter is more so than the former. In all of these species 
there is on the lateral slopes in the anterior half of the interior a more or less con- 
spicuous wrinkling of the shell which may represent the vascular markings of other 
species of Lingula. 
Formation and locality. — Four specimens have been found by Mr. Ulrich in the Hudson River group 
between Wykoff and Spring Valley, Minnesota. 
Lingula canadensis Billings? 
1862. Lingula canadensis Billings. Palteozoic Fossils, vol. 1, p. 114, fig. 95. 
1863. Lingula canadensis Billings. Geology Canada, p. 210, fig. 209. 
1889. Lingula? (Lingulasma?) canadensis Ulrich. American Geologist, vol. iii, p. 384. 
a 
Fig. 26. Copy of Billings' original figure of his Lingula canadensis. 
Original description: "Shell large, oblong, subpentagonal; front margin gently 
convex or nearly straight; anterior angles narrowly rounded; sides straight and 
nearly parallel for about two-thirds the whole length, then converging to the beaks; 
apical angle about 130°; cardinal edges on each side of the beak nearly straight. 
The valves are moderately convex, most tumid in the upper half, descending to the 
sides and front margin with three flat slopes. Surface with fine, thread-like, elevated, 
longitudinal ridges, five or six in the width of one line at the front margin; these 
are crossed by much finer concentric ridges, ten or twelve in one line, which are 
continued over the longitudinal ridges and give to the surface a minutely nodulose 
appearance." 
The material upon which the above identification is based is rather fragmentary, 
consisting of two small broken individuals, and a piece of the lateral portion of a 
large specimen. These are not altogether identical in outline with the figure given 
by Billings, but since the surface ornamentation of L. canadensis is like that of the 
Minnesota specimens it has seemed best to refer them provisionally to this species 
