BRACHIOPODA. 95 



Brachial valve similar in degree of convexity to the opposite valve, slightly ridged 

 from beak to near the center. Beak obtuse and but slightly incurved. 



Pedicle valve regularly convex, most prominent near the center sloping gently to 

 the front and sides. Beak elevated, slightly incurved and truncated by a circular fora- 

 men. Deltidial plates conspicuous. A slight auriculation in the posterio-lateral region 

 gives a shouldered appearance to some individuals, but it is not a constant character. 



Brachial valve similar in degree of convexity to the opposite valve, slightly ridged 

 from beak to near the center. Beak obtuse and but slighly incurved. 



Measurements: The average of a number of mature individuals give the following: 

 Length, 42 millimeters; breadth, 40 millimeters; thickness, 17 millimeters." 



Remarks — The material from Missouri is fragmentary, but there seem to be no 

 well-marked differences between Greger's Cranaena morsii and Hall and Whitfield's 

 Dielasma calvini. Greger's figures show a wider hingeline and a brachial valve less 

 tapering near the hingeline, but some of the Missouri specimens have this valve of the 

 same shape as the Iowa species. The most characteristic feature of the species is the 

 slight convexity of the valves. 



The retention of the color pattern was mentioned by Greger, and the pattern is 

 shown in figure 5 of plate 18 



Occurrence — Snyder Creek shale of Callaway County. 



Cranaena iowensis (Calvin) 

 Plate 20, figures 20-22 



1890. Terebratula (Cryptonella) iowensis Calvin, Bull. Lab. Nat. Hist. Univ. Iowa, I, 



p. 174, pi. 3, fig' 4. 

 1894. Cranaena Iowensis Hall and Clarke, Pal. New York, VIII, pt. II, p. 297, pi. 



80, figs. 36-39; pi. 83, fig. 4. 

 1897. Cranaena iowensis Schuchert, U. S. G. S. Bull. 87, pi. 188. 

 1911. Cranaena iowensis Cleland, Wisconsin Geol. Nat. Hist. Surv. Bull. 21, pi. 72, 



pi. 13, figs. 8-11. 

 1914. Cranaena iowensis Weller, Mississippian Brachiopoda, p. 249, figs. a.-j. 



Calvin's description — "Shell large, ovate, widest at or below the middle, adult 

 specimens very convex, greatest convexity a short distance in front of the umbo; front 

 margin regularly rounded, truncate or slightly sinuate. Dorsal valve convex, curving 

 gradually in all directions from a point situated at a variable distance behind the middle 

 of the valve. Ventral valve, like the dorsal, sloping from a point behind the middle 

 line, the curvature increasing most rapidly toward the beak; beak only moderately in- 

 curved, perforated by a relatively small foramen; cardino-lateral slopes rounding gradu- 

 ally, without the usual subangular ridge toward the deltidial plate; deltidial plate wide, 

 its sides meeting beneath the foramen in an obtuse angle; muscular scars of ventral valve 

 elongated and bounded by sharp ridges that leave three grooves extending beyond the 

 middle of the shell in the exfoliated cast, middle groove deeper than the other two and 

 extending in some instances almost to the front margin; sometimes the middle groove 

 widens from the beak to about the middle of the valve, then narrows abruptly and is 

 continued toward the front as a slender furrow. Muscular markings on the dorsal 

 valve very variable; in general, the scars were long and separated by a narrow carina. 

 The other details, however, are far from being constant. Dental laminae forming two 

 short septa in the umbonal cavity of ventral valve, nearly parallel or slightly diverging 

 where their lower margins join the shell, but curving at their upper margins so as to 

 conform nearly in direction to the lateral margins of the deltidial plate. Surface smooth, 

 marked only by obscure lines of growth. Shell very finely punctate. Internal loop 

 unknown. 



Large specimens are an inch and a quarter in length, more than an inch in width, 

 and three-fourths of an inch in thickness. Immature forms are very common." 



