CRUSTACEA. 97 



Dimensions. The only individuals observed in which the parts arc not 

 detached, measure as follows: 



a- Body. Cephalon. Thorax. • Pygidium. 



Length 52 mm. 20 mm, L5 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. 21mm. 18 nun. 



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 he found in relative 

 proportions and the number and character of the pygidial annulations. 



Distribution. In the sandstone at Pendleton, Indiana, associated with l'n>,///s 

 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, 



