692 THE PALEONTOLOGY OF MINNESOTA. 
[Krausella inaqualis. 
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 2. 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 Beecherellide. 
KRAUSELLA INZQUALIS, 2. Sp. 
PLATE XLIV, FIGS. 44—46. © 
SizE.—Length 2 3mm.; hight 1.17 mm.; thickness 0.8 mm. 
s 
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 xttv. 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.—Lower Trenton limestone, Dixon, Illinois. (Stone’s River group, Vanux- 
emia bed). 
KRAUSELLA ARCUATA, ”. SD. 
PLATE XLIV, FIGS. 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. inequalis. The 
posterior spine also is more slender and situated lower, the point in some instances 
being almost on a line with the ventral edge of the right valve. Finally, the left 
valve is more uniformly convex, the upper half of the surface being fuller, while the 
