PLATE XVb. 



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



Legen<i. j. Cjiiiiiiial piocess. ' r. Difluctor scare, 



a. Adiluctor scars. 



Genus STKOPHEODONTA, Hall. 



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

 Page 284. 



Stropheodonta (Douvillina) arcuata, Hall. 



Fi{^. 1. The inteiior of a peilicIe-valve ; shdwinjr the cavity in the canlinal area aa left by the removal of 

 the caniinal process, the thickened, sharply defined ami elevated muscular area. 



Kijif. 2. The intei-ior of the brachial valve. 



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

 divei'gent muscular ridges. X 2. 



Uppei- Devonian, Lhne Creek, Iowa. 



StROPHEODONTA VARIAlilUS, Calviii. 

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

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



Upper Devonian. Lime Creek, Iowa. 



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 interior of a brachial valve ; showing the muscular ridges. 

 Chemung group. Tioga county, Pennsylvania. 



StROPHEODONTA (DoUVILLINA ?) IN^QUISTRIATA, Hall. 



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

 pression. 



Hamilton group. Canandaigua Lake, iV. Y. 



Genus STROPHONELLA, Hall. 



(See Plate XII.) 

 Page 290. 



Strophonella c^lata, Hall. 



Fig. '10, The interior of a brachial valve in an unusually tine state of pi-eservation. The flabellate muscular 

 scars have the f<ii-m usual to Ibis genus and similar to that characterizing Douvillina. The 

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

 frequent occiu'rence in many of the earlier species of Sthopheodonta. The impressions of the 

 pallial sinuses are also distinctly shown. 



Chemung group. Near Addison, N. T. 



Genus CHONETES, Fi.scher de ^^'ALDHEIM. 



(See Plate XVI.) A ' .',','■ 



Page 303. 



Chonetes Flemingi, Norwood and Pratten. 



Fig. II. The intei-i.r of a pedicle-valve ; showing the character of the muscular sears and the internal 

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

 Coal Measures. IlUnoVi. 



Chonetes Smithi, Norwood ami I'raltcu. 

 Fig. 12. The interior of a brachial valve ; showing the four scais of the a(l<hictor muscles. X 2. 

 Coal Measures. Illinois. 



