274 



NORTH AMERICAN INDEX FOSSILS. 



Niagaran ? of Falls of Ohio Region. 

 Scotia. 



Upper Siluric of Nova 



225. C. laqueatum Conrad. Siluric. 



Large, trigonal or trapezoidal and very ventricose ; pedicle 



valve twice as long as deep, with scarcely incurved but projecting 



beak ; brachial valve shallower. Pli- 

 cations rounded to subangular,more 

 iliilll widely spaced towards lateral mar- 



gins where they disappear. 



Niagaran of Indiana, common. 



LXVI. Stricklandinia Billings. 

 Usually large. Valves nearly 

 equal. Pedicle valve with a short 

 median septum in the interior sup- 

 porting a small and short spondy- 

 lium. Hinge line straight, cardinal 

 area present on each valve and beak 

 of pedicle valve not highly arched ; 

 otherwise very similar to Conch- 

 idinm. Siluric. 





332. Conchidium nettelrothi. 

 Nettelrotb. 



226. S. davidsoni Billings. Siluric. 



Longitudinally ovate, f inch-3 inches long with width about \ 



less. Front of shell narrowed to a linguiform extension. Beaks 



^ IG - 333- Stricklandinia caste liana. (After Hall and Clarke. ) 



only slightly developed. Pedicle valve often with a faint median 

 sinus in youth, becoming obsolete with age, often developing into 

 a fold. Brachial valve with a fold widening into the linguiform ex- 



