PLATE XVb. 



(Figures 1-9, 14-19, 21, '.'i.as-SO, 32-35 by G. B. Simpson; 10-13,21-26, 36, 37 by R. P.Whitfield; 20,23,27, 31 by E. Emmons.) 



Legend, j. Ciinlinal process. r. Diductor scai-s. 



a. Adductor scars. 



Genus STEOPHEODONTA, Hall. 



(See Plates XIII, XIV, XV, XX.) 

 Page 284. 



Stropheodonta (Douvillina) arcuata, Hall. 



F\g. 1. The interior of a i:ieilicle- valve ; .showing the cavity in the cardinal area as left by the removal of 

 the cardinal proce.ss, the thickened, sharply defined and elevated muscular area. 



Kijf. 2. The interior of the brachial valve. 



Fig. 3. The same enlai'ged, to show the character of the cardinal process, the small crural plates and 

 divergent musculnr ridges. X 2. 



Upper Devonian, Lime Creek, Iowa. 



Stropheodonta variabilis, Calvin. 

 Figs. 4, 5. Opposite sides of the same specimen ; showing the contoui- and surface ornamentation. X 2. 

 Fig. 6. The interior of the brachial valve ; showing the cardinal process and divergent muscular ridges. 

 X 2. 



Upper Devonian. Lime Creek, luwa. 



Stropheodonta (Douvillina) Cayuta, Hall. 



Fig. 7. The interior of a pedicle-valve ; showing the sharply defined, thickened and elevated muscular 



area and its subdivisions. 

 Fig. 8. The intei-ioi' of a brachial valve ; showing the muscular ridges. 

 Chemung group. Tioga county. Pennsylvania. 



Strophkooonta (Douvillina ?) iN.a5QuiSTRiATA, Hall. 



Fig. 9. The interior of a pedicle-valve ; showing the greatly thickened lateral margins of the muscular im- 

 pression 



Hamilton group. Canandaigua Lake, N. Y. 



Genus STROPHONELLA, Hall. 



(See Plate XII.) 

 Page 290. 



Strophonella c^lata, Hall. 



Fig. '10, The intei'ior of a brachial valve in an unusually fine state of jire.servation. The flabellate muscular 

 scars have the form usual to this genus and .similar to (hat chai-acterizing Douvillina. The 

 crenulations of the hinge-line do not extend to the extremities of the cardinal area ; a feature of 

 fi'equent occurrence in many of the earlier species of Stropheodonta. The impressions of the 

 pallial sinu.ses are also distinctly shown. 



Chemung group. Near Addison, N. Y. 



Genus CHONETES, Fi.scher de Waldheim. 



(See Plate XVI.) 

 Page 303. 



Chonetes Flemingi, Norwood and Pratteu. 



Fig. 11. The interi-r of a pedicle-valve ; showing the character of the muscular scars and the internal 

 opening.s of the sjiine-tutjes beneath the cardinal area. X 3. 

 Coal Mea.sures. Illinois. 



Chonetes Smithi, Norwood and Piatten. 

 I'"ig. 12. The interior of a brachial valve ; showing the four scars of the adductor muscles. X 2. 

 Coal Measures. IlUnois. 



