Beedk.] Carboniferous Invertebrates. 157 



Schizodus subcircularis. 



Schizodus subcircularis Herrick, Bull. Den. Univ., n, p. 41, pi. in, f. 24, 



(18S7 . 

 Schizodus subcircularis Girty, U. S. Geol. Surv., xix, pt. in, p. 582, pi. 



i.xxn, f. 8a, (1899). 



Herrick's description (in part) : ". . . The anterior and 

 lower margins are continuous parts of almost a circle, which 

 is only a little produced posteriorly ; the posterior margin is in- 

 clined ; beak submedian, posterior umbonal ridge not sharp. 

 The shell is moderately convex and is nearly smooth, except for 

 the distant lines of growth. Length, 0.63 inch ; width, 0.59 

 inch; convexity (single valve) , about 0.20 inch." 



Range and distribution : Upper Coal Measures ; Lawrence. 



A single right valve from the dam rock at Lawrence agrees 

 well with Herrick's figure and description. It is a little smaller 

 and, apparently, better preserved than Herrick's specimen, for 

 it shows excedingly fine, inconspicuous concentric Btrise in addi- 

 tion to the distant lines of growth mentioned in his description. 



Schizodus compressus, n. sp. Plate XXII, figs. 6, 6d. 



fSChizodu8 whi eleri Herrick, Bull. Den. Univ., n, p. 42, pi. in, f. 15,(1887 ). 



Shell medium size for this genus, not very convex, elongate 

 subovate in outline, cuneate posteriorly. Antero-dorsal mar- 

 gin non-sinuate ; anterior margin broadly rounded ; ventral mar- 

 gin quite convex, terminating posteriorly in a rather prominent 

 acute angle ; posterior margin obliquely truncate ; dorsal mar- 

 gin nearly straight, curving very slightly upward. Hinge line 

 straight, a little less than one-half the length of the shell. 

 Beaks depressed, incurved, inconspicuous, scarcely elevated 

 above the hinge line, located about one-third the length of the 

 shell from the anterior end. Umbonal slope subangular, 

 rather prominent, becoming obsolete towards the posterior 

 angle of the shell. (Greatest convexity of the shell below and 

 slightly behind the umbo. Posterior to the umbonal slope 

 the shell is much compressed. Adductor scars small, sub- 

 elliptical in shape, anterior one situated near and a little above 

 the middle of the anterior margin ; posterior one placed close 

 to the dorsal margin, a little behind the beak. Pallial line sub- 



