692 THE PALEONTOLOGY Or MINNESOTA. 



[Krausella InaecLiialis. 



Beecherella ovata is too imperfectly known to be referred to any genus definitely, 

 but B. navicula and B. angularis are generically distinct from B. carinata as well. as 

 from B. subtumida and the species of Krausella. Leaving out B. ovata. we have then 

 at least three and" probably four, more or less closely related generic groups, which 

 it seems to me may be justly referred to collectively as the Beecherellidce. 



Keausella in^qualis, «. sp. 



PLATE XLIV, FIGS. «-46. 



Size.— Length 2 3 mm.; hight 1.17 mm.; thickness 0.8 mm. 



Carapace elongate-subelliptical, the ventral outline longer and straighter than 

 the dorsal, the ends, excluding the posterior spine, subequal and most prominent in 

 the lower half; outline in a ventral view elongate rhomboidal, in an end view sub- 

 triangular, the lower part being very thick. Valves thick, very unequal, the larger 

 (left) strongly overlapping the other; basally the left valve turns inward abruptly, 

 causing a decided flattening of the ventral edge; right valve moderately convex, 

 with the dorsal and ventral margins subparallel, the dorsal edge being less curved 

 than in the left valve; behind it is drawn out into a strong blunt spine-like process, 

 the point of which extends a short distance beyond the edge of the opposite valve. 

 Surface of valves without markings of any kind so far as, observed. 



This is a well marked species, distinguished chiefly . by the great ventral 

 thickness and relatively high position of the posterior spine. The latter may be 

 a little lower and the dorsal outline somewhat more convex than in the specimen 

 illustrated on plate xliv. The inequality of the two valves is so great that, 

 unless found in their natural position, they would scarcely be suspected of belonging 

 together. 



Formation and locality.— Lowbt Trenton limestone, Dixon, Illinois. (Stone's River group, Vanux- 

 emia bed). 



Krausella aecuata, n. sp. 



PLATE XLIV, FI&S. 47—53. 



Size.— Length 1.9 mm.; hight 0.82 mm.; thickness about 0.58 mm. 

 Length 1.7 mm.; hight 0.70 mm, 

 Length 1,8 mm.; hight 0.70 mm. 



In this species the outline is nearly semicircular or semielliptical, the basal line 

 being straighter and the dorsal margin more arcuate than in K. incequalis. The 

 posterior spine also is more slender and situated lower, the point in some instances 

 being almost on a line with Jbhe ventral edge of the right valve. Finally, the left 

 valve is more uniformly convex, the upper half of the surface being fuller, while the 



