PLATE XVb. 



(Figures 1-9, 14-19, 21, 22, 28-30, 32-35 by G. B. SIMPSON; 10-13, 24-26, 36, 37 by R. P. Whitfield; 20, 23, 27, 31 by E. EMMONS.) 



Legend, j. Cardinal process. r. Diductor scars, 



a. Adductor scars. 



Genus STROPHEODONTA, Hall. 



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

 Page 284. 



Stropheodonta (Douvillina) arcuata, Hall. 



Fig. 1. The interior of a i^edicle-valve ; showing the cavity in the cardinal area as left by the removal of 

 the cardinal process, the thickened, shaiply defined and elevated muscular ai'ea. 



Fig. 2. The intei'ior of the brachial valve. 



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

 divei'gent muscular ridges. X 2. 



Upper Devonian, Lime Creek, Iowa. 



Stropheodonta variabilis, Calvin. 



Figs. 4, 5. Opposite sides of the same specimen ; showing the contour and surface oi-namentation. X 2. 

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

 X 2. 



Upper Devonian. Lime Creek, I<-rwa. 



Stropheodonta (Douvillina) Cayuta, Hall. 



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



area and its subdivisions. 

 Fig. 8. The interior of a brachial valve ; showing the muscular ridges. 

 Chemung group. Tioga county, Pennsylvania. 



Stropheodonta (Douvillina ?) ln^quistriata, Hall. 



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

 pression. 



Hamilton group. Canaiidaigua Lake, N. Y. 



Genus STROPHONELLA, Hall. 



(See Plate XII.) 

 Page 390. 



Strophonella c^lata, Hall. 



Fig. ;"10. The interior of a brachial valve in an unusually fine state of preservation. The flabellate muscular 

 scars have the form usual to this genus and similar to that characterizing Docvillina. The 

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

 frequent occurrence in many of the earlier species of Stropheodonta. The impressions of the 

 pallial sinuses are also distinctly shown. 



Chemung gi-oup. Near Addison, N. Y. 



Genus CHONETES, Fischer de Waldheim. 



(See Plate XVI.) 

 Page 303. 



Chonetes Flemingi, Norwood and Piatten. 



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

 openings of the spine-tubes beneath the cardinal area. X 3. 

 Coal Measures. Illinois. 



Chonetes Smithi, Noi'vvood tuid Piatteu. 



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

 Coal Measui-es. Illiiiois. 



