BRACHIOPODA. 185 



f // Shell piano- or bi-convex. 



XXVIII. Billingsella. 



k. Surface radially plicate 666. 



666. Plications coarse, radially striate XL. Meekella. 



666. Plications not radially striate , ss. 



ss. Entire surface pustulose. Shell small CXIX. Vitulina. 



ss. Spines irregularly distributed on the crests of the plications. 



XXIX. Nisusia. 



ss. No spines or pustules present l8f. 



i8f Shell distinctly punctate 18*. 



1 8* Plications sharp XXX. Protorthis. 



1 8* Plications rounded XCIV. Tropidoleptus. 



i8f Shell not distinctly punctate.. 19* 



19* Shell very small, cyrtiniform (cardinal area of 



pedicle valve very high) LX. Scenidium. 



19* Shell comparatively large. 



XXVIII. Billingsella. 



k. Surface spinose (productoid) 777 



777. Pedicle umbo prominent and strongly incurved tt. 



it. Shell small XLV1. Productella. 



tt. Shell large XLVII. Productus. 



777. Pedicle valve not strongly incurved, often truncate. 



XLV. Strophalosia. 



k. Surface smooth except for concentric growth lines 888. 



888. Margins of hinge area vertically grooved. 



XXXIII. Pholidostrophia. 



888. Margins of hinge area not grooved uu. 



uu. Hinge line short. Umbo usually conspicuous. No spon- 



dylium, large delthyrium XXVI. Kutorgina. 



uu. Hinge line long. Umbo inconspicuous ; spondylium present. 



LXI. Syntrophia. 

 4. Shell orthoid — Shell usually piano- or bi-convex, never definitely concavo- 

 convex. Hinge line usually much less than the greatest width of the 

 shell. Cardinal areas well and almost equally developed in each valve ; 

 triangular delthyrium usually well developed in each valve and open. 

 Median sinus when present generally very broad and ill defined. Sur- 

 face marked with radiating striae or plications /. 



/. Surface radially plicate (z. e., radiating lines coarse) 999 



999. Hinge line short, forming about one third the greatest width 



of the shell. Shell globular LVIII. Enteletes. 



999. Hinge line long vv. 



vv. Pedicle valve flat or partly concave; brachial convex. 



L. Dinorthis. 



vv. Pedicle valve convex 19I. 



I9f Brachial valve flat 20*. 



20* Deltidium present in pedicle valve Vj ff . 



I7 // Spines absent g // . 



g" Shell punctate... XXVIII. Billingsella. 

 g" Shell impunctate XXX. Protorthis. 



