12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



DESCRIPTION OF PLATE P 



PAGE 



Paterina prospectcnsis (Walcott ) 6 



Fig. I. (X2.) Large dorsal valve. Plesiotype. U. S. Nat. Mus., Cat. 

 No. 7^2>77- 

 2. ( X 2.) Ventral and dorsal valves. Plesiotype. U. S. Nat. Mus., 

 Cat. No. 78378. 



Mesonacis frcinonti (Walcott) 6 



Fig. 3. Fairly well preserved cephalon. The course of the posterior 

 facial suture, the marginal suture, the occiptal and intergenal 

 spines, and the general shape of the cranidium, together with 

 the slightly advanced position of the genal spines, are clearly 

 shown. Plesiotype. U. S. Nat. Mus., Cat. No. 78379. 



4. Another cephalon in which the anterior margin on the left is 



disturbed by the peculiar slickensiding in the fossils from 

 this locality. Size and position of the eyes and character of 

 glabeller furrows are well shown. Plesiotype. U. S. Nat. 

 Mus.. Cat. No. 78380. 



5. A third, less complete cephalon, well preserved on the right side, 



showing particularly the posterior facial and intramarginal 

 sutures as well as the striations on the rim. Plesiotype. U. S. 

 Nat. Mus., Cat. No. 78381. 



6. Small cephalon with left eye practically complete. Plesiotype. 



U. S. Nat. Mus., Cat. No. 78382. 



7. Mould of portion of cephalon and thorax. Note extra width of 



third segment. Plesiotype. U. S. Nat. Mus., Cat. No. 78383. 



8. ( X 4-) Enlargement of genal angle of specimen illustrated in 



preceding figures, showing striated rim and course of the intra- 

 marginal suture across the genal angle. 



9. The associated hypostoma, referred to the species. Plesiotype. 



U. S. Nat. Mus.. Cat. No. 78384- 



^ All figures natural size unless otherwise stated. 



