I \MKI.I. ii. i:\\. Ill \ 



ui. nlfMiil 1 



The .-prcie- ma\ !'e compared with I Millin- M.ill. -p. I 



inn'i Saltord. -p.. I ml \ . uinlxmntn. V.i ..... f tli ..... f..mis, howc 



seem to me sutliciently similar .-r the separation of the i 



troublesome. 



' 



M:- 



\ \M.\tMlA 

 I-I.XTI \\\\ II I I XXXVIII. I IU. tt. 



i..iu. I 'i i;i. M, 1892. Nln.-t..-nth Ann. !:.[ Minn, | 



Shi'll a little above tin 1 ii)f<liiiin -i/.e. known only from casts of the interior, an. I 

 the impression of the hinge ami free margins on the limestone matrix. The outline 

 was rabrfaomboklftl, with the cardinal and anterior margins nearly straight, and the 

 t\\.. line- forming an angle of about r.j-'; anterior extremity subacuate or sharply 

 ronndeil, hin^e line e.|iialin^ nearly three-fourths of the entire length, postero-ventral 

 margin l-roadly rounded, almost semicircular: aliove this the posterior outline is some- 

 what >traightened and slopes forward rapidly, meeting with the cardinal line to form 

 an angle of ahout \'.\' : the iminediate junction liowever is not perceptibly angular. 



In the oa.sts the beaks project strongly, are nearly terminal, pointed, slightly 

 incurved, greatly compressed, and somewhat twisted. A strong sulcus extends from 

 the beaks to the postero-basal part of the casts; this sulcus occupies the larger part 

 of the anterior slope, and from its inner side the umbonal ridge, constituting the 

 highest portion of the surface, rises abruptly. For the reasons mentioned the 

 anterior slope appears flattened and in p.irt concave, while the posterior is air 

 uniformly convex to the margin. Cardinal slope abrupt, especially near the hinge. 



(iiitta-perdia impressions bring out the internal characters in a very satisfactory 

 manner. They show a wi.lt? and faintly .-triated ligamental area, two lateral and 

 two cardinal teeth, both pairs large and distinctly crenulated on the sides. The 

 cardinal pair are considerably curved and the lower one forms the upper boundary 

 of the very ,-harply impressed anterior miiM-ula (in the whole the hinge 



impre.e> one as being unusually strong. The posterior muscular scar is large, 

 ovate, slightly prolonged below and but faintly impressed. 



Comparing casts with the associated I', nhfusin-nna. which is nearer than any. 

 other now known, the presei: M its greater oblijuit\ 



anterior end, much stronger umbonal sulcus. and be 1 ned ligamental 



area, and stronger as well a- more coarsely crenulated binge teeth. 



mntion and totality . Blue Uimwtoni- <<f t: at Minneapolis, Mlnoe*ota. 



f. Key. No. 8336. 



