56 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



lens-area in the cast is elliptical ; and there are about five lenses, in the 

 central vertical lines, and laterally about twelve or thirteen rows, with a 

 single lens in the posterior angle. 



The glabella is strongly tuberculated ; the cheek-border in the lower side 

 strongly denticulated, as many as seven denticulations between the antero- 

 lateral extension of the glabella and the posterior angle of the border ; the 

 posterior angle rounded, with a short spine or node-like process about half- 

 way between the eye and the posterior margin. 



Geological formation and locality. In the limestone of the Upper Hel- 

 derberg group : Helderberg mountains, Albany county, N.Y. 



PHACOPS CACAPONA (n.s.). 



In some collections obtained many years since from a friend in George- 

 town, D.C., are two specimens of Phacops, labelled " from the mouth of 

 Capon river, near its junction with the Potomac." These specimens are 

 clearly distinct from any species in New- York : they are partial casts, but 

 preserve some of the surface-characters. The glabella is short and wide, and 

 three tubercles are preserved in the occipital furrow. The eyes are much 

 elevated : there are seven lenses in many of the vertical rows, and nineteen 

 rows may be counted laterally, the one in the posterior angle having two 

 lenses. The body is broad, the width in a coiled specimen being equal to the 

 length : the axis is comparatively broad and rounded, nearly as wide as the 

 lateral lobe. The caudal shield is undeterminable. The surface of the sla- 

 bella is marked by rounded tubercles, which are distributed with some degree 

 of regularity. 



The proportions of the body are distinguishing features ; but the form 

 of the eye, the number and arrangement of the lenses are more distinctive, 

 when compared with either of the other species. The specimens are converted 

 into a reddish grey siliceous material. 



This species may perhaps be identical with that sent by Prof. Ducatel 

 to Prof. Brongniart, and indicated by him as Calymene macrophthalma; 

 but the specimen figured on Plate i, fig. 4, of the "Crustaces fossiles," is 

 certainly not identical with this one. 



The large specimen (a cast in plaster sent by Dr. Hosack), indicated by 

 M. Brongniart as coming from the United States, is the original of Prof. 

 GtREEn's Calymene anchiops, a Dalmania as already indicated in this 

 paper. 



When compared with the cast of P. Info of Green, the greater propor- 

 tional breadth becomes a distinguishing feature, and the glabella is much 

 less produced anteriorly. The form and proportions of the eye in the cast 

 do not furnish any means of comparison. 



Geological formation and locality. The locality named " Mouth of the 

 Capon river near the Potomac," indicates a geological horizon of the Upper 

 Helderberg or Hamilton group. 



[ September, 



