OSTRAGODA. 661 
Eurychilina subradiata.] 
inner side of the valve, we see nothing of the outer wall of the marginal area. The 
last I regard as the most important difference, since, if the facts are correctly repre- 
sented in Prof. Jones’ figures it would remove his species from the typical section of 
Eurychilina to that distinct group of species which is defined on a preceding page 
in the remarks following the generic description. 
Variety rncuRvVA, n. var. Plate xttv, Fig. 2. 
This subordinate name is proposed for a variety of this species that is rarely 
associated with more typical specimens in the upper third of the Trenton shales, the 
highest horizon in which this species is known to occur. The variety is a little 
smaller than full grown specimens of the typical form, and more rounded in the 
posterior outline. More striking differences however are seen in the marginal 
area. This, instead of being concave and curved outward, is convex and incurved, 
its width is less and more equal, the radii very indistinct and the terminal border 
more sharply defined. These differences produce a form closely resembling the 
Kentucky species E. granusa. We except of course the ornamentation, the two being 
very different in this respect. . 
Formation and locality —Ranges from the lower Trenton limestone to the upper third of the Tren- 
ton shales; Minneapolis, St. Paul, Cannon Falls, and near Fountain, Minnesota. The species is not 
abundant anywhere, only about twenty specimens in all having been seen. Variety tnewrva occurs as far 
as known only at St. Paul. 
EURYCHILINA SUBRADIATA Ulrich. 
PLATE XLIV, FIGS. 3, 4, 4a. 
Eurychilina subradiata ULRICH, 1890. Jour. Cin. Soc. Nat. Hist., vol. xiii, p. 126. 
SizE.—Without marginal area, length 1.75 mm.; hight 0.9 mm.; thickness 0.50 mm. 
With marginal area, length 2.32 mm.; hight 1.3 mm. 
Body of valves almost exactly semicircular in outline, with the surface highest 
along an obtuse ridge-like prominence, running lengthwise across the central portion 
of the valve and from the summit of which the surface descends with a distinctly 
concave slope to the thickened dorsal edge; on the opposite or ventral side the slope 
is more gently concave or flat; anterior extremity compressed; sulcus deep and 
unusually wide, beginning a little within the dorsal margin and extending half way 
across the body, its lower and posterior margins thickened and sharply defined; just 
back of the sulcus a large round tubercle; surface appearing smooth in some speci- 
mens, but usually it is pitted as shown in fig. 4. Marginal area nearly flat, the inner 
edge rising abruptly and forming a low, sloping wall around the body, the outer 
edge formed by a sharply elevated narrow border; posterior and ventral portions of 
area holding about the same width, but at the anterior end it is usually much less; 
external surface of area with more or less obscure radial furrows. Inner side of 
