CRUSTACEA 99 



Dimensions. An average individual affords the following measurements: 



Body. Ceph Thi rax. • rlium. 



Length 43 mm. L6 mm. M nun. L3 mm. 



■■- 



Width 23 mm. 23 mm. 23 mm. 21 



mm. 



The largest pygidium observed has a length of 22 mm. and a width of 35 

 mm., the smallest a length of 9 mm. and a width of 15 mm. 



Distribution. In the sandstones at Pendleton. Indiana, associated with the 

 preceding species. 



Proetus crassimarginatus. 



PLATE XX, FIGS. 6-8, 30-31 ; PLATE XXII, FIGS. 30-36 ; AND PLATE XXV, FIG; - 



rmem crassimarginatws, Hall. Geology of N. Y., Survey of Fourth Geol. Dist., p. 17-J. lij;. 5. 1843 

 /',-, ilus crassimarginata, Hall. Twelfth Rept. N. V. State Cab. Nat. Hist., p. 88. 1859. 

 PhUlipsia crassi ' Canadian Journal, p. 362. 1861. 



rginatus, Ham,. Descr. New Species of Fossils, etc., p. 72. 1861. 

 s crassimarginatus, Hall. Fifteenth Rept. N. V. S Nat. Hist., p. 100. 1862, 



Proetus crassimarginatus, Hall. Illustrations of Devonian Fossils, pi. xx, figs. 20-31. 1876. 

 Proetus Conradi, Hall. Illustrations of Devonian Fossils, pi. xx. figs. 5, 8, 9. 1876. 



General Form and Proportions. Body regularly ovate, margins evenly 

 tapering from the base of the cephalon to the narrow posterior extremity. 

 Length to width at base of cephalon, as 2 to 1. 

 Surface convex and strongly trilobate. 



Cephalon semicircular in outline, border broad, strongly recurved in front. 

 more depressed and flattened at the sides, and produced at the genal angles 

 into a broad, flat spine. Length to width as I to 2. 



Facial Sutures normal. 



Glabella large, sub-quadrate, semi-ovoid, narrowing slightly toward the 

 anterior extremity ; length equal to five-sixths the Length of the cephalon, 

 and width more than one-third that of the cephalon. Surface very convex. 

 slightly flattened above; sides rising abruptly from the shallow marginal 

 furrows. External evidence of the lateral furrows wanting. A single speci- 

 men from which the test has been so far weathered as to leave only a thin 

 film near the lower surface, shows four pairs and the accessory furrows, of the 



