208 MISSISSIPPIAN BRACHIOPODA 



valves present, from a fine grained, compact limestone which resembles, 

 lithologically, bed No. 4 of the Kinderhook at Burlington, Iowa. The 

 other two examples are from the porous brown limestone of bed No. 7 of 

 the same section. In the original description the species is recorded from 

 ' ' the base of the Burlington Limestone, ' ' which, from a consideration of 

 the specimens, should doubtless be interpreted as Kinderhook. 



Girty 1 has figured a shell under the name Camarophoria ringens which 

 is of the type of White 's Rhynchonella caput-testudinis. This shell clearly 

 has the outline suggested by the original definition of R. ringens, and 

 similar specimens have not infrequently been identified with Swallow's 

 species by collectors in the Mississippi Valley, although they commonly 

 possess a smaller number of plications than Swallow designates. This 

 type of shell can scarcely be considered as representative of Swallow's 

 species, however, because no example of it has ever been observed by re- 

 cent collectors in the cherts from which R. ringens is said to have been 

 collected. 



Horizon. Kinderhook. 



RHYNCHOTETRA OVATUM (Greger) 

 Plate XXVII, Figs. 16-20 



1910. Paraphorhynchus ova-turn Greger, Am. Jour. Sci. (4), vol. 29, 

 p. 74, figs. 9-10. 



Description. Shell of medium size or somewhat larger, subovate in 

 outline, longer than wide, the greatest width near the mid-length, the 

 posterior extremity usually acutely pointed, the line of junction between 

 the valves deeply and strongly serrate. The dimensions of a nearly per- 

 fect specimen, one of the cotypes, are : length of pedicle valve 35.5 mm., 

 length of brachial valve 33.3 mm., greatest width 26.8 mm., thickness 

 18 mm. 



Pedicle valve gently convex throughout the greater portion of its sur- 

 face, its greatest depth near the middle, abruptly deflected towards the 

 opposite valve near the postero-lateral margins, the deflected surface 

 nearly flat and lying nearly at a right angle to the plane of the valves 

 or slightly concave and somewhat inflected to the margin towards the 

 cardinal extremities ; mesial sinus obscure or essentially obsolete, when 

 best develoved it is broad, only slightly depressed, and restricted to the 

 extreme anterior part of the valve; beak not prominent, pointed, only 

 moderately incurved; surface of the valve marked by from sixteen to 

 twenty, usually simple, strong but rather low, radiating plications, 

 rounded on top and separated by rounded furrows, most of them orig- 

 inate near the beak, only rarely arid upon some specimens never do they 

 increase by division or implantation upon the body of the valve. 



iMon. U. S. Geol. Survey, vol. 33, pt. 2, pi. 69, figs, la-b (1889). 



