PLATE XXXVIII 



PAGE-, 



Figs. 1-5. HEBEBTELLA VULGABIS Raymond 239' 



1-2. Three views of a small specimen with direct striae. X 1.5. 

 4, 5. A large specimen exhibiting some bifurcating striae. X 2. 

 Ordovician (Chazyan), Chazy, New York. 



Figs. 6-8. DINOBTHIS (PLAESIOMYS) PLATYS (Billings) 247' 



6. Brachial valve. 



7. Edge view of shell. 



8. Pedicle valve. 



Ordovician (Chazyan), Montreal, Canada. 



Figs. 9-12. HEBEBTELLA BOBEALIS (Billings) 238. 



9-11. Three views of a specimen. 



12. An example with very short hinge line. 



Ordovician (Chazyan), near Montreal, Canada. 



Figs. 13-15. TETBADIUM SYBINGOPOBOIDES Ulrich 200 



13. Surface of a weathered slab showing usual aspect of the species. 



14. Portion of the same illustrating tubes in more detail. X 3. 



15. Drawing of a transverse section illustrating the usual appearance 



of the tubes (at the top), the development of the characteristic 

 four septa (in the middle), and two tubes still united (at bottom 

 of figure). X 6. 



Ordovician (Chazyan), upper part Stones Rives Is., Pinesburg 

 Station, Maryland. 



Figs. 1-5, 9-12 are after Raymond and 6-8 are after Billings. 



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