258 Annals of the Carnegie Museum. 



3. The same species. Exterior of pedicle valve. X 2. Carnegie Museum. 

 ' 4. Orthis costalis Hall. Photograph of holotype. American Museum Natural 

 History. 



5. Orthis ignicula Raymond. A small specimen in Professor Hudson's col- 

 lection. 



6, 7. The same species. Brachial and pedicle valve of the holotype. More 

 than twice natural size. Carnegie Museum. 



8-10. Orthis acutiplicata Raymond. Three specimens from the lower part 

 of the Chazy at Valcour Island. X 2. Carnegie Museum. 



11. Plectorthis exfoliata Raymond. A pedicle valve. This was one of Hall's 

 types of Orthis costalis. American Museum Natural History. 



12. The same species. The brachial valve of a small specimen in Professor 

 Hudson's collection. 



13. 14. Plasiomys plalys (Billings). Photographs of a brachial and pedicle 

 valve from the Middle Chazy at Sloop Bay, Valcour Island, New York. Natural 

 size. Carnegie Museum. 



15, Valcourea strophomenoides Raymond. Interior of a pedicle valve from 

 the Middle Chazy at Plattsburgh, New York, X 2. Carnegie Museum. 



16, 18. The same species. Drawing and photograph of the interior of a brachial 

 valve. The drawing is X 2. Same locality as the last. 



17, 19. The same species. Drawing and photograph of the interior of a pedicte 

 valve. Drawing X 2. On the same block with 18 and 19 may be seen the exteriors 

 of other specimens of this same species. 



Plate XXXVI. 



1. Valcourea strophomenoides Raymond. Dorsal view of an entire specimen 

 from Plattsburgh, New York. X 2. Carnegie Museum. 



2, 3. Hebertella vulgaris Raymond. Dorsal view of one specimen, and pedicle 

 valve of another. 2 is from the Upper Chazy and is in Professor Hudson's collec- 

 tion, and 3 is from the Lower Chazy, and is in the Carnegie Museum. 



4. The same species. Interior of a brachial valve. X 2. Professor Hudson's 

 collection. 



5. Cast of the interior of the pedicle valve of the same species. Such specimens 

 as this are often identified as Orthis costalis. Professor Hudson's collection. 



6. 7. Hebertella imperalor (Billings). Casts of the interior of a brachial and 

 a pedicle valve from the Aylmer sandstone at Aylmer, Quebec. Natural size. 



8, 9. Hebertella bellariigosa (Conrad). Dorsal and cardinal views of a specimen 

 from the Upper Chazy at Valcour Island, New York. Photograph by Professor 

 Hudson of a specimen in his collection. 



10, II. Clitambonites multicostus (Hudson). An entire specimen from Professor 

 Hudson's collection. X 2. 



12-14. The same species. Photographs of two interiors and one exterior of 

 brachial valves. All in Professor Hudson's collection. 



15, 16. Clitambonites porcia (Billings). Pedicle valve of the holotype. X 2. 

 Museum of the Geological Survey of Canada. 



17. Orlhidium ? lamellosum Raymond. A pedicle valve from the base of 

 the Upper Chazy at Sloop Island. Holotype. X 2. Yale University Museum. 



