GAMAROTCECHIA lOd 



The species has sometimes been referred to the genus Pugnax, but such 

 reference is incorrect. Besides being quite different from typical mem- 

 bers of that genus in external characters' it possesses a crural cavity sup- 

 ported by a median septum at the base of the divided hinge-plate a char- 

 acter which is typical of the genus Camarotcechia. 



Horizon. Salem limestone. 



CAMAROTCECHIA GROSVENORI (Hall) / 

 Plate XXIV, Figs. 61-72 



1856. Rhynchonella Grosvenori Hall, Trans. Albany Inst, vol. 4, p. 10. 



1882. Rhynchonella Grosvenori Whitfield, Bull. Am. Mus. Nat. Hist., vol. 



1, p. 53, pi. 6, figs. 31-34. 



1883. Rhynchonella grosvenori Hall, 12th Ann. Rep. Geol. Surv. Ind., 



p. 331, pi. 29, figs. 31-34. 

 1895. Pugnax Grosvenori Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60. 



figs. 13-17. 

 1901. Wilsonia Grosvenori .Whitfield and Hovey, Bull. Am. Mus. Nat. 



Hist., vol. 11, p. 388. 

 1906. Pugnax grosvenori Beede 30th Ann Rep Geol. Surv. Ind., p. 1305, 



pi. 22, figs. 31-34. 

 1910. Wilsonia grosvenori Weller, Bull. Geol. Soc. Am., vol. 21, p. 510, 



fig. 11- * 



Description. Shell small, subglobular in form, the width equal to, 

 greater than or less than the length, the greatest width near or in front 

 of the mid-length, the postero-lateral margins gently convex or nearly 

 straight, meeting at the beak in an angle of 90 degrees or less, the ante- 

 rior and antero-lateral margins more or less regularly rounded. The di- 

 mensions of a large individual are : length 7 mm., width 6.5 mm., thick- 

 ness 5.5 mm., width of sinus in front 4.5 mm. 



Pedicle valve more or less regularly convex throughout, the surface 

 curving somewhat more abruptly to the postero-lateral margins, arched 

 from beak to front ; for a short distance on each side of the beak the edge 

 of the valve along the postero-lateral margins is somewhat abruptly and 

 sharply inflected to form a small pseudo-cardinal area ; mesial sinus obso- 

 lete in the posterior half of the shell and sometimes obsolete throughout, 

 usually it is broad and slightly depressed anteriorly and is produced an- 

 teriorly in a broad lingual extension which is curved towards the opposite 

 valve to such an extent that its surface lies at nearly a right angle to the 

 general plane of the valve in front ; beak pointed, a little incurved and 

 projecting posteriorly beyond the hinge-line; delthyrium broadly trian- 

 gular, partially closed by deltidial plates, with a subcircular foramen at 

 the apex which encroaches to some extent upon the beak of the valve ; 

 plications simple, rounded, from 18 to 22 in number, two or three of which 

 on each side near the cardinal margins are very small, from three to six 

 are included in the mesial sinus, four or five being the more usual num- 



