SPIRIFER 317 



Brachial valve less convex than the pedicle, the greatest depth a little 

 posterior to the middle, becoming a little compressed towards the car- 

 dinal extremities; cardinal area very narrow and linear; mesial fold 

 originating at the beak, where it is bounded by rather strong furrows but 

 is not elevated above the surface of the valve on either side, anteriorly 

 it continues to be sharply defined by the stronger furrows but is con- 

 spicuously depressed to the front, being scarcely elevated above the 

 surface of the lateral slopes, it is marked by four subequal, rounded 

 plications, all of which originate through the subdivision of the original 

 one at the beak; each lateral slope marked by simple plications which 

 are entirely similar in form and number to those of the opposite valve. 



The minute surface markings are not well preserved upon the specimens 

 observed, but the concentric lines of growth are inconspicuous, com- 

 monly being restricted to a few faint ones near the margin of the shell. 



Remarks. The original type of this species was never illustrated and 

 the specimen itself has been lost, and from the original definition alone 

 it would be difficult to determine the status of the species. In the col- 

 lection of Mr. D. K. Greger, however, a specimen is preserved accom- 

 panied by a label written by Swallow himself. This specimen is con- 

 sidered to be authentic and it agrees in all essential respects with the 

 original definition. The specimen which is illustrated herewith, and 

 which has been used in the preparation of the above description, agrees 

 in all essential respects with the authentic example in the Greger col- 

 lection. The species is a small one, although it grows considerably 

 larger than the specimen whose dimensions have been given, and is 

 characterized especially by its rotund form, there being little or no 

 compression of the pedicle valve towards the cardinal extremities, and 

 the mesial fold of the brachial valve being depressed to such a degree 

 that it scarcely interrupts the general convexity of that valve. The 

 species is evidently not a common form. 



Horizon. Chouteau limestone. 



SPIRIFER PLATYNOTUS n. sp. 

 Plate XXXIX, Figs. 1-10 



1901. Spirifer marionensis Weller, Trans. St. Louis Acad. Sci., vol. 11, 

 p. 188, pi. 16, figs. 16-17. 



Description. Shell below medium size, subsemicircular to broadly 

 sub-triangular in outline, greatest width along the hinge-line, cardinal 

 extremities more or less acutely angular. The dimensions of two pedicle 

 valves are: length 16 mm. and 15.5 mm., width along the hinge-line 

 25 mm. 'and 42 mm., convexity 8 mm. and 7.5 mm., height of cardinal 

 area 3.5 mm. and 3.5 mm. The dimensions of a brachial valve are : length 

 16 mm., width along the hinge-line 38 mm., convexity 6.5 mm. 



