CRUSTACEA. 
97 
Dimensions. The only individuals observed in which the parts are not 
detached, measure as follows: 
a. Body. Cexihalon. Thorax. Pygidium. 
Length_ 52 mm. 20 mm, 15 mm. 17 mm. 
Width_ 29 mm. 29 mm. 27 mm. 24 mm. 
b. 
Length _ 38 mm. 14 mm. 12 mm. 12 mm. 
Width_ 25 mm. 25 mm. 21 mm. 18 mm. 
Observations. In the form and furrows of its glabella, and in the contour of its 
pygidium, this species presents some points of similarity to Proetus macrocepha- 
lus, of the Hamilton group. The rapidly tapering and deeply furrowed glabella 
makes its earliest appearance here and is not exemplified by any other species 
as yet known in the Upper Helderberg formations. Proetus Haldemani is also a 
close congener, but in these forms specific differences will be found in relative 
proportions and the number and character of the pygidial annulations. 
Distribution. In the sandstone at Pendleton, Indiana, associated with Proetus 
latimarginatus and Conocardium cuneus, a horizon probably corresponding in age 
with the Schoharie grit of New York. 
Proetus latimarginatus, n. sp. 
PLATE XXII, FIGS. 7-12. 
General Form and Proportions. Outline elliptical, length to width as 2 to 1. 
Surface conspicuously trilobate, convex, deflected on the marginal area. 
Cephalon semi-elliptical in outline; border broad, flat, thickened by doublure 
and produced into stout spines at the angles of the cheeks. Length to 
width as 5 to 7. 
Facial Sutures taking their origin close within the genal angles, passing 
forward very obliquely over the occipital ring to the eye-lobe, cutting the 
anterior margin at points relatively distant, and approximating upon the 
doublure. 
