180 NORTH AMERICAN INDEX FOSSILS. 



Sinus and fold prominent, in typical forms surface with plicae gen- 

 erally coarse i. 



i. Fold and sinus absent in. 



III. Large, with talse area, no spondylium. LXXXV Peregrinella. 



III. Small, with spondylium LXXII Camarophoria. 



i. Fold and sinus present 222. 



222. Plications moderately developed on the lateral slopes or wanting, 



prominent centrally and anteriorly, no spondylium jj. 



jj. Sinus exceedingly prominent LXXXII. Pugnax. 



jj. Sinus moderately prominent LXXVIII. Leiorhynchus. 



222. Plications absent from the umbo,sponydium well developed, kk. 

 kk. Plications roughened by strong concentric growth lines. 



LXXII. Camarophoria. 



kk. Plications smooth 6f. 



6f Shell very small (about ^ inch long). 



LXII. Camarella. 



6f Shell moderately large LXIII. Parastrophia. 



222. Entire shell covered with plications or striations //. 



//. Both umbos very prominent, that of the brachial valve the 

 more conspicuous, well marked spondylium in pedicle 



valve LXIV. Anastrophia. 



II. Umbo of pedicle valve the more prominent 7f. 



7f Pedicle umbo very closely incurved over the brachial. 5*. 

 5* Plications marked anteriorly by a faint median line. 



Shells ventricose, no spondylium 5 // - 



5 /r Median septum and cardinal process in brach- 

 ial valve well developed. 



LXXIX. Uncinulus. 

 $" Cardinal process absent... LXXX Wilsonia. 

 5 7/ Median septum in brachial valve very faint. 



LXXXI. Hypothyris. 

 5* Plications not marked anteriorly by a median line. 



6". 

 6 // Pedicle valve with obscure muscular scars and 

 well-marked spondylium. 



LXXII. Camarophoria. 

 6 r/ Pedicle valve with prominent muscular scars 



without spondylium b" . 



b // Brachial valve with median septum. 2 /// . 

 2 7// . Septum excavated posteriorly ; 

 teeth supported by lamellae ; no 

 cardinal process. 



LXXVI. Camarotozchia. 

 2 /// . Septum not excavated ; strong 

 recurved teeth without lamella; 

 slender cardinal process. 



LXXIV. Rhynchotrema. 



b" . Brachial valve without median septum. 



LXXVII. Stenochisma. 



7f Pedicle umbo projecting, not very closely incurved over 



the brachial, commonly showing deltidial plates and 



foramen 6*. 



