PLATE IX Continued. 



OLENELLUS HOWELLI 30 



Fig. 15. View of a specimen fully developed, excepting the presence of an ocular ridge, 

 and the distance of the eyes from the glabella. The genal spines are too short 

 in the figure. Natural size. 



15 a. Natural-size view of a head -having the genal angles carried forward; eyes 

 without an ocular ridge, and the angles of the posterior margin strongly 

 marked. 



15b. The head of a young individual, enlarged to four diameters, in which the embry- 

 onic features are still more prominent. See plate xxi, figs. 1-9. 



15 c. Fragments of thoracic segments associated with this and the following species. 



OLENELLUS GILBERTI.. 29 



Fig. 16. View of a large head, Natural size. See plate xxi, fig. 13. 



16 a. Fragment showing the glabella and a portion of the palpebral lobes. Natural size. 



ANOMOCARE ? PARVUM 59 



Fig. 17. Enlargement of the specimen described to five diameters. The outline of the pos- 

 tero-lateral limb probably extends laterally a little more than in the figure. 



PTYCHOPARIA (?) LINNARSSONI 47 



Fig. 18. View of the broad form of the head, exclusive of the free cheeks, X 2. 

 18o. View of the narrow form, similarly enlarged. 



DlCELLOCEPIIALUS ? EXPANSU8 45 



Fig. 19. View showing the character of the glabella and the peculiar ridges crossing the 

 anterior portion of the fixed cheeks, enlarged to one and one-half diameters. 



PTYCHOPARIA (?) PROSPECTENSIS 46 



Fig. 20. View of the type specimen, enlarged to three diameters. The furrow crossing the 

 glabella at the second pair of glabellar furrows is not seen in the specimen. 



PTYCHOPARIA (PTEROCEPHALUS ?) OCCIDEXS 58 



Fig. 21. The test is largely exfoliated from the surface of the glabella, and but one pair of 

 furrows are shown ; figure enlarged to three diameters. 



OGYGIA. ? ? SPINOSA 63 



Fig. 22. View showing the central portions of the head. Natural size. 



AGRAULOS GLOBOSUS 61 



Fig. 23. A minute, very convex head, enlarged to four diameters. 



DlCELLOCEPHALUS ? QUADRICEPS 45 



Fig. 24. Small head, enlarged to three diameters. 



DlCELLOCEPHALUS OSCEOLA 40 



Fig. 25. View of specimen identified with the Wisconsin species. Natural size. 



PTYCHOPARIA ANYTUS 56 



Fig. 26. Central portions of the head, enlarged three diameters. The fixed cheeks are more 

 elevated at the outer termination of the ocular ridges than represented. 



ARETHUSINA AMERICANA 62 



Fig. 27. View of central portions of head ; the ocular ridges are stronger than in the figure; 

 enlarged to three diameters. 



PTYCHOPARIA (E. ) DISSIMILIS 51 



Fig. 28. View of fragment showing the central portion of the head. Natural size. 



