116 MISSISSIPPIAN BRACHIOPODA 



septum extends some distance, its entire length not shown in the only 

 specimen observed. 



Remarks. The example of this species whose dimensions are given 

 above is an undersized specimen, some large shells having an extreme 

 length of 65 mm. or more. The type specimen of the species, from the 

 Burlington limestone, is here illustrated for the first time, but the species 

 also occurs, perhaps even more commonly, in the Keokuk limestone. 



The species is characterized by its large size, its small auricular exten- 

 sions, its somewhat flaring anterior and lateral margins, and especially by 

 the large groups of fine, closely crowded spines which occur on the lateral 

 slopes adjacent to the cardinal extremities. 



Horizon. Burlington and Keokuk limestones. 



PRODUCTUS CRAWFORDSVILLENSIS n. sp. 

 Plate XII, Figs. 4-7 



1892. Productus magnus Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 

 17 A, fig. 15 (not P. magnus M. & W.) 



Description. Shell above medium size, broader than long, the greatest 

 width along the hinge-line, the anterior margin slightly sinuate, the vis- 

 ceral cavity between the two valves rather shallow. The dimensions of a 

 nearly complete pedicle valve are : length from hinge-line to front margin 

 36.6 mm., length from umbonal region to front margin 41.8 mm., width 47 

 mm., convexity 30 mm. 



Pedicle valve strongly convex, the longitudinal curvature subgeniculate 

 a little back of the line between the visceral and produced portions of the 

 valve, the posterior slope gently convex with the umbonal region only 

 moderately protuberant beyond the hinge-line, compressed towards the 

 cardinal extremities, the anterior slope gently convex, the surface drop- 

 ping abruptly to the lateral margins, the auriculations small and com- 

 pressed vertically; mesial sinus originating near the middle of the pos- 

 terior slope, rather narrow, shallow and rounded in the bottom, lying in 

 the middle of a rather broad region which is gently convex on each side 

 of the sinus and drops away rather abruptly into the lateral slopes ; the 

 beak small, incurved, but scarcely reaching ( beyond the hinge-line. Sur- 

 face marked by rounded, radiating costa 3 which increase by frequent 

 bifurcations and intercalations upon the posterior slope, dividing less 

 frequently or sometimes anastomosing upon the anterior slope and be- 

 coming niore or less obsolete towards the front of mature examples, where 

 best developed upon the anterior slope they are usually about 1 mm. 

 apart from center to center; the posterior slope of the valve is well 

 marked by concentric, wrinkle-like markings, giving it a distinctly semi- 

 reticulate appearance, these markings often being more strongly defined 

 towards the cardinal margin ; the entire surface is marked by fine but per- 



