PLATE VI. 



Cyrtodontarca ? gouldii. Page 152. 



l-lc— Views of valves. 1 and Ic are right valves, la and 16 are right 

 valves, all showing nature of dentition, as best it can be shown, under the 

 beaks of the casts. The specimens are tilted at various angles to show the 

 teeth, which accounts for the variety of peculiar forms. 



Ic. —Appearance of right valve showing two lateral teeth. Nos. 69, 68, 

 52, 54, and 70, respectively, of Whitehorse collection. 



2, 2a. — Specimens referred provisionally to this species, though they are 

 probably distinct from it. 2a shows the dentition. Nos. 50 and 51, White- 

 horse collection. 



Cyrtodontarca ? parallelidentata. Page 153. 



3-3c.— Four specimens of this species. No. 3 shows the general aspect of 

 the cast of the shell, somewhat broken; 3a and 36, two right valves en- 

 larged, showing, poorly, the nature of the dentition; 3c is the left valve, 

 showing the dentition much better. Enlarged. Whitehorse collection. 



Cyrtodontarca ? multidentata. Page 153. 



4, 4a.— Left and right valves, showing dentition. Enlarged. Nos. 55 

 and 56, Whitehorse collection. 



Cyrtodontarca ? sp. 



5. —A specimen, the dentition of which is not preserved, showing the 

 nature of the surface markings. X 3/2. No. 101, Whitehorse collection. 



Cyrtodontarca ? sp. 



6. —An incomplete specimen, dentition not shown. No. 55a, Whitehorse 

 collection. 



Myalina sp. Page 156. 



7. — Fragment of valve, natural size. No. 74, Whitehorse collection. 



Pleurophorus ? albequus. Page 160. 



8.— Left valve of specimen, showing radiating ribs and a strong, more 

 backward-curving ridge in the shell than normal, with correspondingly sharp 

 beak. No. 42, Whitehorse collection. 



8a. —Right valve of a young specimen, possibly of the variety longus 

 of this species, showing lateral posterior hinge tooth. No. 41, Whitehorse 

 collection. 



86.— Enlarged beak of left valve of cast, showing impression of hinge 



(over) 



