NIAGARA CROUP. 303 



In some specimens the entire surface is, as described by MuRCinsoN, covered by thin im- 

 bricating lamellffi with waved edges. In other specimens this character is only visible around 

 the margin of the buckler and caudal shield, and to some extent on the extremities of the 

 articulations, while the central and higher parts of the surface are granulated or punctate. 



In specimen fig. 5 of the plate, the entire surface, except the margins, is beautifully punctate ; 

 while in some other specimens this character is not observed, or only combined with the 

 lamellose strice. The punctate character appears to be secondary, and to result from the ex- 

 foliation of an outer crust, which is granular ; and the entire exfoliation of the crust sometimes 

 leaves a punctate surface beneath. 



Fig. 1 & 2. Young specimens of this trilohite. 



Fig. 3 & 4. Larger specimens of the same, showing slightly different proportions. 



Fig. 5. A larger individual where the articulations of the body are closely pressed together, and 



the cephalic shield slightly overlapping the upper edge. 

 Fig. 6. A large individual preserving its natural proportions. 

 Fig. 7 & 8. The central portions of the cephalic shield as they occur in the shale, entirely 



flattened. 

 Fig. 9. An unusually large cephalic shield, preserving the cheeks which are somewhat distorted. 

 Fig. 10. The cheek with a part of the eye attached, and the same enlaaged. 

 Fig. 12. A part of the caudal shield and two articulations enlarged, showing the lamellar striss 



with intermediate granular surface. 

 Fig. 13. A portion of another caudal shield of another specimen, preserving the punctate crust 



in one part, showing the striated surface where the crust is broken off" around the 



margin, and above this the punctate surface, which sometimes marks well preserved 



casts. 

 Fig. 14 & 1'5. Enlargements of the punctate surface of the shell and cast of this fossil. 



Position and locality. In the shale at Lockport, and rarely in the limestone above. Frag- 

 ments have been found at Rochester and other places. 



670. 4. PHACOPS LIMULURUS. 



Pl. LXVII. Fig. 1 -8. 

 Asaphus limulurus. Green, Monograph, 1832, p. 48. 



Compare Trilobus caudatus, Brpnnich in Ki.neb. Selsk. Skrivt nya Saml. I, 1781, p. 392, n. 3. 

 " Asaphus caudatus, Brongniart, Crust. Fossiles, 1822, pag-. 22, pi. 2, fig. 4 a, b, c, d- 

 " Trilobus caudatus, Schlotheim, Nachtroege, 1823, pag. 35, no. 11 (p. 21, 4). 

 " — — Parkinson, Organic Remains, Vol. iii, pi. 17, fig. 17. 



" Asaphus caudatus, Dalman, Palreaden in Vet. Acad. Handl. 1826, pag. 236, 2, and 



296, 2, pi. ii, fig. 4. 

 " — — HisiNGER, Pelrcf. Suec. 1837, p. 13, t. ii, f. 2. 



" A. longicaudatus, Murchison, Sil. System, 1839, pag. 653, pi. 14, fig. 11, 12, 13 & 14. 

 " Phacops caudatus, Burmeister, Pl. iv, fig. 9 : not description and citations same 

 author, p. 94. 



