""'* PjIl^ontology of new-yoek. 



Not Bntomostracitus caudatus, Wahlenberg, Nov. Act. Soc. Sci. Upsal. 1821, pag. 28, pi. ii, 

 fig. 3. 

 " j^saphus mucronatus, Brongniart, 1. c. p. 24, t. iii, f. 9. 

 " — — Dalman, Hisinger, loc. cit. 



" y/. tuberculocaudatus , Murchison, loc. cit. 

 " Phacops mucronatus, Emmkrich. 



Buckler sublunate, with the spines at the posterior angles extended ; front extended in a 

 short obtusely angular point; glabella lobed ; anterior lobe broad, separated from the three 

 smaller lobes on each side by a broad oblique furrow, which communicates with the longitudinal 

 furrow separating the cheeks from the glabella ; lower lobes separated by sharp transverse 

 grooves, the lower lobe continuing across the centre in a slightly defined ridge ; eyes of medium 

 size, the base opposite the two upper of the three small lobes of the glabella ; facial suture 

 extending to the margin of the shield, on a line with or a little above the base of the eyes ; 

 body with eleven articulations, axis broadest in the middle, the articulations with thickened 

 obtuse terminations, but not tuberculate ; articulations of the lateral lobes deeply grooved 

 from the base more than two thirds of their length, and having the extremities bent rather 

 abruptly downwards ; caudal shield with the central lobe consisting of fifteen articulations, 

 which terminate in an elevated obtuse point below ; lateral lobes with eight articulations, all 

 except the upper one grooved throughout their whole length till they are merged in a thickened 

 border ; this thickened border, extending along the two sides of the pygidium, is united below 

 the termination of the central lobe, and extended into a long spinelike process ; entire surface 

 granulated. 



This species has produced much confusion in the attempts to identify it with European 

 species, and we are not at this time any more certain of its identity or difference than we were 

 ten years since. I have had no opportunity of seeing a veritable specimen of P. caudaius of 

 Europe, and therefore have not made a direct comparison which could decide the question. I 

 have been inclined to believe that a part of the specimens figured by Brongniart are identical 

 with our species, as is the pygidium figured by Dalman and Hisinger, as well as A. (Phacops) 

 longicaudatus of Murchison, but not Jl. tuberculato-caudatus of that author. The figure of 

 BuRMEiSTER Certainly very much resembles ours, but he cites descriptions and figures which 

 can not be intended for our species. 



M. DE Verneuil has regarded the Niagara species as closely allied to P. mucronatus or 

 P. longicaudatus of Murchison ; but I am not inclined to adopt his view, for several reasons ; 

 for although P. mucronatus and P. longicaudatus may be identical, yet specimens, of P. 

 mucronatus from Geinitz in Bohemia, when compared with ours, show the front of the glabella 

 to be broader, equalling or exceeding its length, and with no extension in front ; the anterior 

 portion is of different form, and separated on the lower side by a scarcely oblique sharp groove 

 or furrow, while in ours it is broad and oblique. The anterior of the three small lateral lobes of 

 the glabella is similar to that of P. limuluriis ; the middle or second one is narrowed at its 

 extremities, and the lower one is rounded or nucleiform, and narrowed at its base, almost 

 separating from the axis ; while in P. limulurus the middle lobe is not narrowed at the ex- 



