PLATE 67. 



Fig. 1-8. G70. 4. PiiACops LiMuLiiRus. {Pag. 303.) 



1. An individual of Ihv ordiiKiiy .sine of lliis species, in itic Niagara group. 



2. A sni;mcr individual. Tliis, lilvc all tliu young s|iccinuuis I have seen, is narrowed towards the posterior 



part of the body, more than older speeiuieus. 



3. The separate cephalic shield, destitute of the crust, whidi is of very common occurrence in localities where 



perfect specimens are not found. 



4. The caudal shield preserving the crust, and the extension of the same into a long slender spine. 



5. A specimen of shale covered with fragments of trilobites and other fossils, among which are two caudal 



shields of this species preserving the crust. 



6. The caudal extremity and a few articulations of the abdotnen from which the crust is separated, showing 



the difference of form thus produced in this part of the fossil. 



7. The inner surface of the crust (separated from the specitnen fig. 0), showing the extension laterally in a 



thick border beyond the marks of articulation, atid posteriorly into the .spine. 



8. The eye of this species enlarged, showiug the elevation, form and structure of the surface. 



Fig. 9, 10. G67. 5. Ceraurus insignis. ( Pag. 306.) 



9. The central portion of a cephalic shield, preserving the form and proportions of the glabella and the outer 



crust in part, with the spine at one of the posterior angles. 



10. Another similar fragment, wlicrc the base of the eye is preserved on oue side, with the posterior spine of 



the buckler. 



Fig. 11, 12. 671. 7. Calymene blumenbachii, tiar. niagakensis. (Pag. 307.) 



11. An entire individual of the largest size, found in the shale of the Niagara group. 



12. A fragment of shale having upon its surfiice three entire specimens of this species. At a tlicrc is the 



caudal shield of a llo.M.VLo.soTt;s, and at b tlie caudal shield of Pliacops timiilurus. 



Fig. 13, 14. 676. 2. Proetus? stokesii. (Pag. 316.) 



13. An individual in soft shale, with the crust partially exfoliated. 



14. An individual in limestone, partially foUled, and having the buckler imperfect. 



Fig. 15. 67.5. 1. Pkoetus corycceus. (Pag. 315.) 



Fig. 16. 677. 1. Beyrichia symmetrica. ( Pag. 317.) 



Specimen natural si/.e and enlarged. 



Fig. 17-21. 678. 2. Cythekina spinosa. ( Pag. 317.) 



17. A fragment of calcareous shale covered with these shells, showing the internal surface. 



18. An enlargeiueut of a single iiuiividual, showing the ordinary appearance of the interior under a magnifier. 



19. A tVagnient covered wllb shells of this species, showing the external surface, with a few of those showing 



the interior. 



20. The exterior of a single individtuil, much enlarged, 



21. The interior, showing the spine projecting beyond the dorsal margin. 



