554 THE PALEONTOLOGY OF MINNESOTA. 



[Vanuxemia obtusifrons. 



thickening of its shell in the umbonal and anterior parts. The beak is compressed 

 in the cast, very prominent and not at all incurved; the anterior muscular scar 

 strongly defined, large, of subcircular form with the inner side truncated; the pallial 

 line is distinguishable all around and, for some distance beneath the anterior muscle, 

 strongly defined by a deep and unusually wide furrow, out of which the anterior 

 side of the body of the cast rises very abruptly. Ligamental area high and strongly 

 striated longitudinally; cardinal teeth strong, comparatively long and slightly 

 curved, three in number; posterior lateral teeth three, strong and a trifle more 

 oblique than the cardinal teeth. Dorsum of cast broad and flat. 



The external characters of the shell ^are unknown, but as the species doubtless 

 belongs to the most typical section of the genus, they will probably prove much as 

 in V. inconstans, V. dixonensis and V. rotundata. 



Formation and locality. Middle third of the Trenton shales, St. Paul. Minnesota. 



VANUXEMIA OBTUSIFRONS Ulrich. 



PLATE XXXVIII, PIGS. 15-19. 



Cypricardites obtusifrons ULKICH, March 3, 1892. Nineteenth Ann. Rep., Geol. and Nat. Hist. Sur. 



Minn., p. 233. 

 Cypricardites vicinus SARDESON, April 9,_1892. Bull. Minn. Acad. Nat. Sci., vol. iii, p. 339. 



Shell rather large, moderately ventricose, very oblique, subovate, much the 

 highest and broadly rounded posteriorly, with the beaks subterminal, incurved, not 

 very prominent nor large, and the umbones strongly rounded. Anterior end obtuse, 

 the upper part forming nearly a right angle with the hinge line, the slightly project- 

 ing junction between the two lines rather sharply rounded; postero-basal half of shell 

 broadly semielliptical; dorsal outline very gently concave. Surface markings con- 

 sisting of irregular, fine and coarse, sublamellose lines of growth. 



Casts of the interior with the beaks large, very prominent, compressed and 

 strongly incurved at their apices; umbonal ridge and sulcus of moderate definition, 

 nearly parallel with the anterior margin. Anterior muscular scar large and strongly 

 defined, excavated out of the-hinge plate, in the cast having the appearance of a strong 

 process projecting from the under side of the base of the beak forward and upward 

 to the anterior extremity of the hinge; posterior scar illy defined, large, ovate, situ- 

 ated close to the posterior end of the hinge. Pallial line distinct. 



Hinge with three cardinal and three posterior lateral teeth in each valve, both 

 sets strong. The cardinal teeth are situated under the beaks, finely toothed on 

 their sides, slightly curved and usually oblique, ranging at an angle of 45 or more 

 with the hinge line.* 



The original (Inure of the Interior of this species It faulty In its representation of the cardinal teeth. The type 

 specimen has been Injured at tills point and In euch a manner that T quite overlooked the actual remains of the 



