1897.] KEW YORK ACADEMY OF SCIENCES. 257 



Rhynchonella mutata Hall. (?) 



PI. XIX., figs. 13-15. 



1858. Rhynchonella mutata. Hall, Geol. Iowa, Vol. 1, pt. 2, p. 

 658, PI. 23, figs. 2a-b. 



1882. Bhi/nchonella mutata, Whitfield, Bull. Am. Mus. Xat. 



Hist., Vol. 1, p. 52, PI. 6. figs. 43-45, 



1883. Rhynchonella mutata, Hall, 12tli Ann. Rep. Geol. Surv. 



Ind., p. 332, PI. 29, figs. 43-45. 



Shell small, subcirciilar in outline. 



Pedicle valve flattened toward the beak, ornamented by thir- 

 teen angular plications, three of which are contained in the 

 mesial sinus, which is deeply impressed toward the front of the 

 shell. 



Brachial valve more ventricose than the pedicle, most rotund 

 on the umbo, ornamented with plications corresponding to those 

 in the pedicle valve. 



There is some doubt about the identification of this species, 

 as it is represented by a limited number of specimens, most of 

 which are fragmentary, 



Spirifer Keokuk Hall, 

 PI, XIX., figs. 10-12. 



1858. Spirifer Keokuk,B.^\\, Geol. Iowa, Vol, 1, pt, 2,p. 642, PI. 



20, figs. 3a-d, 2d. 

 1858. Spirifer Keokuk, var. Hall, Geol, Iowa, Vol. 1, pt, 2, p, 



676, PI, 24, figs. 4a-d, 

 1891. Spirifera Rockymontana ? Whitfield, Ann, N. Y, Acad. 



Sci., Vol. 5, p. 584, PI. 13, fisr. 30. 

 1895, Spirifera Rockymontana ? Whitfield, Geol, Surv. Ohio, 



Vol, 7, p. 471, PI. 9, fig. 20, 

 1895. Spirifer Keokuk, Hall and Clarke, Pal, N, Y., Vol. 8, pt. 



2, PI. 30, figs, 21-24. 

 Shell of medium size, variable in outline, from subcircular to 

 transversely subtrigonal. Hinge-line straight, relative length 

 variable, from shorter than the width of the shell below to much 

 extended into more or less mucronate extremities. 



Pedicle valve gibbous in the umbonal region, compressed to- 

 wards the cardinal extremities. Area moderately broad, sharply 

 defined, concave towards the beak, which is moderately incurved. 

 Mesial sinus sharply defined, moderately deep and regularly 

 rounded, including three rounded plications, of which the middle 

 one is the largest; in some cases two additional plications are pres- 



Transactions N. Y. Acab Sci., Vol. XVI., Sig. 17, July 19, 1897. 



