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, lilic all the young specimens I have seen, is narrovi^ed towards the posterior 



part of the body, more than older specimens. 



3. The separate cephalic shield, destitute of the crust, Tifhich 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 tliis part of the fossil. 



7. Tlie inner surface of tlie 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. Tlie 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 ceplialic 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, t^a?-. niagarensis. ( Pag. 307.) 



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



12. A fragment of sliale having upon its surface three entire specimens of this species. At a there is the 



caudal shield of a IIomalonotus, 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. PaoETus corycceus. (Pag. 315.) 



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



Specimen natural size and enlarged. 



Fig. 17-21. 678. 2. Cytherina sriNosA. (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, witli 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. 



I 



