CRANIA 47 



Remarks. This species has sometimes been considered as a synonym 

 of C. rowleyi, but a careful comparison of numerous examples of both 

 species has led to the conclusion that they are certainly distinct. C. blairi 

 attains a larger size than C. rowleyi, which alone, of course, would not con- 

 stitute a good specific character ; but in addition the apex of the brachial 

 valve is more nearly central and its radiating costae are finer, more sharp- 

 ly angular, closer together, and are not infrequently somewhat flexuose 

 distally, and the concentric lines of growth are less conspicuous. 



Horizon. Chouteau limestone. 



CRANIA SPICULATA Rowley 

 Plate I, Fig. 31 



1908. Crania spiculata Rowley, Mo. Bureau Geol. and Mines, vol. 8, 2nd 

 ser., p. 74, pi. 17, figs. 7-10. 



Description. Shell below medium size, subcircular in outline, the holo- 

 type attached to a shell of Syringothyris hannibalensis. The dimensions 

 of the holotype are : greatest diameter 13.7 mm., convexity of brachial 

 valve 5 mm. 



Pedicle valve apparently cemented by its entire external surface, en- 

 tirely covered in the holotype and in other examples observed. 



Brachial valve depressed conical, the apex central and erect, the sur- 

 face sloping in all directions from the apex in straight or gently convex 

 lines. The surface marked by more or less obscure concentric lines of 

 growth and covered by fine, closely crowded papilla? which are slightly 

 elongate radially with their distal extremities more elevated than their 

 proximal, apparently being the bases of fine, appressed spines which have 

 covered the entire surface of the valve in life, but whose length cannot be 

 determined from the fossil specimens studied. 



Remarks. This species may be easily recognized by its finely papillose 

 surface markings. It differs from the similarly marked Burlington lime- 

 stone species, .C. Icevis, in its apparently more nearly circular outline, its 

 more nearly central apex, and in the coarser surface papillae. 



Horizon. Louisiana limestone. 



CRANIA L^EVIS Keyes 

 Plate I, Fig. 33 



18*94. Crania Icevis Keyes, Mo. Geol. Surv., vol. 5, p. 40. 



Description. Shell below medium size, transversely subelliptical in out- 

 line, with the posterior margin truncated. The dimensions of one of the 

 type specimens are : greater diameter or width 17 mm., lesser diameter or 

 length 13 mm., length of posterior truncated margin 10.8 mm., convexity 

 of brachial valve 4 mm. 



Pedicle valve not known. 



