EXPLANATION OF PLATES. 

 Plate 1. 



Fig. 1. — Hudsonaster narrawayi (Hudson) (also see platea 2 and 4). 



A greatly enlarged photograph of the genoholotype of Protopalseaster 

 narrawayi Hudson. The inner ventral side of the specimen ia here seen 

 with all of the dorsal skeleton weathered away except one of the basal 

 supramarginalia. Note the well-preserved oral armature and in places 

 the ambulacralia. The latter are the "covering platea" of Hudson. 



Photograph by Prof. George H. Hudson. 



Middle Ordovicic (Black River). Ottawa, Canada. 



Collection of Mr. J. E. Narraway. 



Plate 2. 



Fig. 1. — Hudsonaster narrawayi (Hudson) (also see plates 1 and 4). 



A photograph X 6 of the actinal side. Note the five long spines (tori) 

 of the oral armature. 



Middle Ordovicic (Black River). Kirkfield, Ontario, Canada. 



Collection of Peabody Museum, Yale University. 

 Fig. 2. — Hudsonaster matutinus (Hall) (also see plates 3 and 5). 



A photograph X 3 of three specimens showing the actinal area as preserved 

 on a piece of black limestone. 



Middle Ordovicic (Trenton). Rathbone Brook, near Newport, Her- 

 kimer County, New York. 



Collection of Museum of Comparative Zoology, Harvard University 

 (No. 26). 



Pl.\te 3. 



Fig. 1.— Hudsonaster rugosus (Billings). 



A photograph X 2 of the abactinal area of a cotype. 

 Upper Ordovicic (Richmondian). Charleton Point, Anticosti Island, 

 Gulf of St. Lawrence, Canada. 

 Collection of the Geological Survey of Canada (No. 1999). 

 Fig. 2. — Hudsonaster matutinus (Hall) (also see platea 2 and 5). 



A retouched photograph X 2 showing the abactinal side. 

 Middle Ordovicic (Trenton). Trenton Falls, New York. 

 Collection of the Museum of Comparative Zoology, Harvard University 

 (No. 3). 

 Fig. 3. — Hudsonaster batheri, new species. 



A diagram X 3 of the actinal aide made from a wax squeeze by Bather, 

 now in the United States National Museum (Cat. No. G0601). 

 Upper Ordovicic. Thraive, Girvan, Scotland. 



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