1890.] NATURAL SCIENCES OF PHILADELPHIA. 167 



little above the middle of each side and connected by a linear band 

 passing around behind." 



Capulus cyrtolites (McChesney). [Plate II, fig. 2.] 



Ptatyceras cyrtolites McChesney, 1800. Desc. New Foss. Pula;. Rocks Western 

 States, p. 71. 



Platyceras cyrtolites Keyes, 1889. Froc. Acad. Nat. Sci., Pliila., 1889, p. 288. 



Capiiliis cyrtolites Keyes, 1890. Am. Geol., vol. V. 



Shell small, slender, arched ; composed of about one volution ; 

 dorsally subangular, with a broad flattened area on each side ; pos- 

 teriorly somewhat plicate. Apical portion small, incurved, some- 

 times enrolled or contiguous. Aperture moderately large, subquad- 

 rangular; lip sharp, sinuous. Surface marked only by strong 

 undulating lines of growth, which are often somewhat imbricated. 



Horizon and localities. Burlington limestone : Burlington, Iowa ; 

 and Calhoun county, Illinois. 



This species appears to be genetically related to C acutirostris 

 (Hall) from the Keokuk and eventually the two forms may prove 

 identical. C. cyrtolites is from the upper division of the Burlington 

 limestone and differs very essentially from any known congeneric 

 species from the same horizon. 



Capulus biserialis (Hall). 



Platyceras biserialis Hall, 1859. Geol. of Iowa, vol. I, pt. ii, Suppl., p. 90. 



Platyceras biserialis Meek & Worthen, 1868. Geol. Sur. Illinois, vol. Ill, p. 

 509. pi. XV, figs. 3a, 3b. 



Capulus biserialis Keyes, 1890. Am. Geol., vol. V. 



Shell rather below medium size, somewhat ovate, subspiral, form- 

 ing slightly more than one volution, regularly incurved. Aperture 

 broadly oval ; margin rather sharp, undulating, with a broad rounded 

 sinus anteriorly. The expanded anterior portion of the shell 

 marked on each side by a longitudinal row of long, conspicuous, 

 hollow spines, about six in number. Surface smooth showing nu- 

 merous fine, sinuous lines of growth. 



Horizon and locality. Burlington limestone : Quincy, Illinois. 



A marked characteristic of this form and also of C. tribulosns 

 (White) is that the tubular spines are arranged in longitudinal 

 rows, while in the few other American spine-bearing Capuli there is 

 no regularity in the distribution of the spinous process. The spines 

 are easily broken and hence are seldom preserved to their full 

 length ; often they are scarcely noticeable. 



