182 Trans. Acad. Sci. of St. Louis. 



illustration, and on account of the greater flattening of the 

 pedicle valve along its median portion toward the front of the 

 shell. In some respects the shell resembles R. dubia of the 

 Spergen Hill fauna, but its hinge-line is longer than in that 

 species. 



SCHIZOPHORIA SUBELLIPTICA (W. & W.). 



PI. XVI. f. 4-5. 



Rhipidomella subelliptica, Bull. U. S. G. S. 153 : 525. 



Original description . " Shell medium size, subelliptical in 

 outline. Hinge line about two-thirds or three-fourths as long 

 as the greatest breadth of the shell. Cardinal extremities 

 rounded, valves subequal, moderately convex ; the pedicle 

 somewhat flattened toward the front, very ventricose on the 

 umbo; beak small and pointed; area about one-third as high 

 as long, delthyrium twice as high as wide. Brachial valve 

 more regularly convex than the pedicle, and the beaks less 

 elevated, very small and pointed, but little incurved." 



" Surface marked by fine, equal rounded striae, which 

 are curved upwards near the extremities of the hinge-line, 

 and some of them run out on the cardinal border. Increased 

 both by bifurcation and implantation." 



Dimensions of an average specimen from the oolite bed : 

 length 10 mm., breadth 12 mm, and convexity of both valves 

 5 mm. 



Remarks. This little shell is a common species in the 

 oolitic bed, and also occurs in the base of the superjacent 

 magnesian limestone. One specimen from this latter horizon, 

 included among the types of the species in the University of 

 Michigan collection, is much larger than any specimen from 

 the oolite, its length being 18 mm., and its breadth 23 mm. 



This species has been referred by Schuchert * to the genus 

 Rhipidomella, but it should rather be referred to Schizophoria. 

 The brachial valve has all the appearance of a diminutive 

 8. swallovi, but the pedicle valve has a higher area and a 

 relatively much more prominent umbo than that species. 



Chonetes logani N. & P. 



PL XVI. f. 10-11. 



Original description. " Shell small; transverse, having its 

 greatest breadth near the cardinal border. Pedicle valve 



* Bull. U. S. G. S. 87 : 352. 



