Beede.j Carboniferous Invertebrate*. 103 



spines when the surface of the shell is perfect." Measure- 

 ments : Length, 19 mm. ; width, 23 mm. ; convexity, 15 mm. 



Range and distribution : Upper and Lower Coal Measures ; 

 Fort Scott, Iola, Lawrence, Topeka, and so on to the base of 

 the Permian. 



The shell varies a great deal in marginal outline, some hav- 

 ing the beak prolonged and sides. somewhat compressed, giving 

 it a very different appearance from the normal form. 



HUSTEDIA. 



Hall and Clarke, Pal. N. Y., VIII, pt. II, p. 120, (1893) : 13th Ann. Rep. N. Y. St. Geol., 



p. 197, (1895). 



Hustedia mormoni. Plate IX, figs. 10-10d: plate X, fig. 3. 



Terrbratula mormoni Marcou, Geol. N. Amer., p. 51, pi. vi, f. 11, (Feb. 



1858): etc. 

 Retzia punetulifera Shumard. Trans. St. L. Acad. Sci., i, p. 220, (Juce, 



1858 i : Meek, Fin. Rep. U. S. Geol. Surv. Neb., p. 181, pi. i, f. 13, pi. v, 



f. 7, (1872); etc. 

 Retzia mormoni Meek and Hayden, Proc. Acad. Nat. Sci. Phil. 1859, p. 



27: etc. 

 Retzia subqlobo*a McChesney, New Pal. Foss., p. 45, (1860): ibid., pi. i, 



f. 1, (1865). 

 Retzia compressa Meek, Geol. Surv. Cal., i, p. 14, pi. n, f. 7, (1864): etc. 

 Retzia radialis Walcott (non Phillips), Mon. U. S. Geol. Surv., vm, p. 



220, pi. 7, ff. 5d-h, (1893); etc. 

 Eumetria punetulifera Derby, Bull. Cornell Univ., i, p. 4, pi. vm, ff. 4, 



5. 7, 8, 10, pi. ix, f. 3, (1874). 

 Hustedia mormoni Hall and Clarke, Pal, N. Y., vm, pt. n, p. 120, f. 196, 



pi. li, ff. 1-9, (1893). 



Meek's description: ''Shell small, ovate; in mature speci- 

 mens, gibbous ; hinge line short, or scarcely extended enough 

 to show distinctly the little ears at the extremities. Ventral 

 valve more convex than the other, the greatest convexity being 

 between the middle and the umbo, which is prominent, rounded, 

 more or less strongly arched, and provided with a moderately 

 large circular foramen ; area well defined, triangular, and arch- 

 ing with the beak. Dorsal valve most convex near the middle ; 

 beak extending a little beyond the hinge margin, and distinctly 

 incurved. Surface of each valve ornamented by fourteen or fif- 

 teen (very rarely sixteen to seventeen) simple, rather prominent, 

 radiating costje, one or two of which are sometimes slightly 

 more depressed than the others, near the front of the ventral 



