SPIKIFER 333 



surface markings, in its greater width and more acute cardinal extremi- 

 ties. Of the specimens figured, the smaller pedicle valve is the more typi- 

 cal. The larger specimen with. the valves in articulation has a much 

 deeper mesial sinus than is usual, but in all other respects it is in full 

 agreement with other representatives of the species. 

 Horizon. Burlington limestone. 



SPIRIFER MUNDULUS Rowley 

 Plate XLIV, Figs. 15-19 



1893. Spirifera mundula Rowley, Am. Geol., vol. 12, p. 307, pi. 14, figs. 

 10-12. 



Description. Shell small, very short and broad, the greatest width 

 along the hinge-line, the cardinal extremities acutely pointed. The di- 

 mensions of a nearly perfect specimen are : length of pedicle valve 8 mm., 

 length of brachial valve 6.2 mm., width along hinge-line 20.5 mm., thick- 

 ness 7.3 mm., height of cardinal area 1.5 mm. 



Pedicle valve prominent in the umbonal region, the surface curving 

 abruptly to the cardinal margin on either side of the beak, convex from 

 the cardinal to the antero-lateral margins and sloping with a gently con- 

 cave curvature laterally from the umbonal region to the cardinal extremi- 

 ties ; mesial sinus originating at the beak where it is a mere groove, con- 

 tinuing to the front as a rather narrow and shallow depression, rounded in 

 the bottom ; beak prominent, pointed, and rather strongly incurved ; car- 

 dinal area of only moderate height, concave, the lateral margins sharply 

 defined and subparallel with the hinge-line for the greater portion of their 

 length. Surface of the valve marked by simple, low, rounded plications 

 which originate along the cardinal margin and are confined to the lateral 

 slopes, from seven to ten occupy each lateral slope, of which those bound- 

 ing the sinus are much the larger. 



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

 ity slightly posterior to the middle, the curvature from the beak to the 

 front along the median line nearly semicircular, the surface sloping from 

 the point of greatest convexity to the cardinal extremities with a gently 

 concave curvature, rather strongly convex from the cardinal margin to 

 the antero-lateral margins; mesial fold well-defined to the beak, rather 

 narrow and only a little elevated above the general convexity of the valve, 

 rounded on top with a very slight longitudinal median groove ; beak small, 

 obtuse, scarcely projecting beyond the cardinal margin. Surface marked 

 by simple, radiating plications entirely similar to those of the opposite 

 valve. 



Surface of both valves marked by rather faint, concentric lines of 

 growth which are somewhat crowded towards the front , margin. 



Remarks. The general aspect of this little shell is more that of a 

 Spiriferina than a Spirifer, but the shell shows no indications of having 



