122 Annals of the Carnegik Muselm. 



characters. Hall, in describing the former species in Vol. II, Pal. 

 N. Y., p. 64, says: "Surfaces covered with fine equal stria; which 

 are equal to the spaces between them : stride round, straight, bifurcating. 

 Three spines on each side of the beak. The species is more flat than 

 the small one in the Corniferous and Hamilton group which it re- 

 sembles." In the nth Indiana Report, ]). 293, Hall says of the 

 same species: ". . . in C. cormita the interstices are wider than 

 the striae, and the latter increase only by interstitial additions below 

 the middle of the shell." The size of the shell, according to Hall's 

 figures, is about 4.2 x 5.5 mm. 



CJwnetes uudulata, in the specimens figured,' has 21 simple striae on 

 the ventral valve and is 3 mm. long by 4. 75 mm. wide. In his descrip- 

 tion Hall says " Surface marked by obscure radiating plications which 

 are broad and rounded below and obsolescent toward the beak : car- 

 dinal margin of the ventral valve ornamented by two diverging spines 

 on each side of the beak. . . . The bases of two spines on each side 

 of the beak are usually preserved and no specimen examined has more 

 than that number." 



Stropholasia truncata Hall. (Plate VII., Rows 3 and 4.) 



Hall, Pal. X. v., Vol. IV, 1867, p. 160, pi. 23, hgs. 12-24. 



Of this species there are about 50 good specimens in the collection. 



There are about as many of one valve as of the other. 



,^--T— ;^_ The largest specimen is 8.33 mm. long and 10 mm. wide : 



\ vJly / The smallest 2.06 X 2.69 mm. All of the specimens 



^- — ^ from this material are small for the species. The smallest 



/', '.' specimen figured by Hall is 10 mm. long and 12 mm. wide 



i>tropnolos 1 a r id j o 



truncata while the largest is 17 mm. long and 18 mm. wide. 

 Hall; dorsal N'epionic Shell. — Owing to the deformation of the ven- 

 beak, show- tral beak and umbo resulting from the method of attach- 

 ing protegu- nient, very little could be made out concerning that valve 

 . . . ,. in the youngest stages except that it is regularly and mod- 

 s^ j5 erately convex. The smallest ventral valve is 2.93 mm. 



long, and 3.33 mm. wide. The beaks of some of the 

 dorsal valves are extremely well preserved and all stages from the 

 protegulum to the adult can readily be observed. The protegulum is 

 transversely oval, with a gently curved hinge. In the best preserved 

 si)ecinien it is .131 mm. long and .156 mm. wide (Fig. 27). 



' Eleventh Ann. Report, Indiana State (ieol., p. 294, pi. 22, fig. 15. 



