306 S. WELLER FAUNA OF THE FERN GLEN FORMATION 



The species is of common occurrence in the Chouteau limestone and has 

 frequently been identified as S. peculiaris, but it may be distinguished 

 from that species by its longer hinge line, its lower and more sharply 

 denned cardinal area on the pedicle valve, and by its more nearly approxi- 

 mate beaks. The types of the species are from the Chouteau limestone 

 of central Missouri and are not illustrated here. The species is an unusual 

 one in the Fern Glen fauna and the example here figured does not exhibit 

 its characters with entire satisfaction. 



SPIRIFER FERNGLENENSIS n. sp. 

 Plate 13, figures 9-10 



Description. — Shell small, subglobular in form, hinge line shorter than 

 the greatest width of the shell, cardinal extremities rounded. Pedicle 

 valve strongly convex, most prominent near the center, the umbo rather 

 small ; beak small, incurved ; cardinal area small and ill defined, the ven- 

 tral margins rounding into the lateral surfaces of the valve; mesial sinus 

 shallow, rather narrow, rounded in the bottom, originating at the point 

 of the beak, not marked by plications; lateral slopes strongly convex; as 

 they approach the lateral and anterior margins the curvature becomes 

 more abrupt, being nearly vertical in the adult shells, each slope marked 

 by about seven broad, flat, and more or less obscure, simple plications. 

 Brachial valve less convex than the pedicle, most elevated near the center, 

 the mesial fold simple, rounded and not strongly elevated, the lateral 

 slopes convex, curving most abruptly to the cardinal margin, marked by 

 plications similar to those of the opposite valve. 



The dimensions of a nearly perfect pedicle valve are: Length, 12.5 

 millimeters; width, 13.5 millimeters; convexity, 5.5 millimeters. 



Remarks. — This species resembles S. choutcauensis, but is smaller and 

 much more rotund in outline, with the beak of the pedicle .valve less 

 prominent and the cardinal area less conspicuous. The dimensions given 

 above are of an average sized individual; the largest example observed 

 has a length of 15 millimeters. The pedicle valve is most commonly 

 preserved ; only a few distorted brachial valves have been met with. 



SPIRIFER PLENUS Hall 



1858. Spirifer plenus Hall, Geology of Iowa, volume 1, part 2, page 603, plate 



13, figures 4a-d. 

 1895. Spirifer plenus H. & C, Paleontology of New York, volume 8, part 2, 



plate 37, figures 32-33. 



Description. — Shell wider than long, but somewhat variable in propor- 

 tions, large individuals becoming more or less subglobose in form ; hinge 



