PLATE 67. 
Fig. 1 - 8. 
670. 4. Phacops limulurus. 
(Pag. 303.) 
1. An individual of the ordinary size of this species, in the Niagara group. 
2. A smaller individual. This, like all the young specimens I have seen, is narrowed towards the posterior 
part of the body, more than older specimens. 
3. The separate cephalic shield, destitute of the crust, which 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 abdomen 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 specimen fig. 6), showing the extension laterally in a 
thick border beyond the marks of articulation, and posteriorly into the spine. 
8. The eye of this species enlarged, showing the elevation, form and structure of the surface. 
Fig. 9, 10. 667. 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, where the base of the eye is preserved on one side, with the posterior spine of 
the buckler. 
Fig. 11, 12. 671. 7. Calymene blumenbachii, vur . niagarensis. (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 surface three entire specimens of this species. At a there is the 
caudal shield of a Homalonotus, and at b the caudal shield of Phacops limulurus. 
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 folded, and having the buckler imperfect. 
Fig. 15. 675. 1. Proetus corycceus. (Pag. 315.) 
Fig. 16. 677. 1. Beyrichia symmetrica. (Pag. 317.) 
Specimen natural size and enlarged. 
Fig. 17-21. 678. 2. Cytherina stinosa. (Pag. 317.) 
17. A fragment of calcareous shale covered with these shells, showing the internal surface. 
18. An enlargement of a single individual, showing the ordinary appearance of the interior under a magnifier. 
19. A fragment covered with shells of this species, showing the external surface, with a few of those showing 
the interior. 
20. The exterior of a single individual, much enlarged. 
21. The interior, showing the spine projecting beyond the dorsal margin. 
