DESCRIPTION OF SPECIES BRACHIOPODA 305 



finely cancellated ornamentation. A few concentric lines of growth of 

 greater or less strength are usually present toward the anterior margin of 

 the shell. 



The -dimensions of a nearly complete example: Length, 56 millimeters; 

 width, 73 millimeters; thickness, ± 40 millimeters; length of hinge line, 

 ±62 millimeters. 



Remarks. — This is a rather common species in the Fern Glen fauna, 

 but it usually occurs in a more or less fragmentary condition. The Fern 

 Glen examples, however, are entirely similar in size and general characters 

 with similarly preserved specimens of the species from the Burlington 

 limestone where the species typically occurs. 



SPIRIFER CHOUTEAUENSIS n. sp. 



Plate 13, figure 11 



Description. — Shell suborbicular in outline, the length and breadth 

 nearly equal, the hinge Mne about two-thirds the greatest width of the 

 shell, cardinal extremities rounded. Pedicle valve strongly convex, 

 prominent on the umbo, the beak small, pointed and incurved over the 

 small more or less ill defined concave cardinal area, the lateral slopes 

 concave toward the cardinal line, convex antero-laterally; sinus of mod- 

 erate depth, continuing to the beak, rounded in the bottom, bounded 

 laterally by rounded plications and marked by from two to four faint, 

 depressed, rounded plications which are formed by the bifurcation once 

 or twice of the lateral bounding plications. Brachial valve less convex 

 than the pedicle, the lateral slopes more or less concave toward the car- 

 dinal line, convex antero-laterally; mesial fold convex, becoming more 

 prominent anteriorly, marked by from two to four plications which are 

 formed by the bifurcation of the single initial one at the beak. The 

 lateral slopes of both valves each marked by from ten to twelve simple 

 rounded plications which are separated by rounded furrows of similar 

 width. 



The dimensions of a specimen of average size are: Length, 19 milli- 

 meters; width, 21 millimeters; thickness, 15 millimeters; length of hinge 

 line, 15 millimeters. 



Remarks. — This species closely resembles 8. suborhicularis of the Bur- 

 lington limestone except in size. It is in most respects a miniature form 

 of that species, adult individuals not attaining a greater length than 25 

 millimeters, while S. suborhicularis grows to be two or three times as 

 large, but the plications of this species are less numerous and those of 

 the fold and sinus are less well defined. The larger species of the higher 

 fauna is doubtless genetically derived from this Kinderhook species. 



