60 MISSISSIPPIAN BRACHIOPODA 



types of the species, which is exceptionally elongate in form, are : length 

 of pedicle valve 28.5 mm., length of brachial valve 27.3 mm., greatest 

 width 27.8 mm., length of hinge-line 26 mm., height of cardinal area 8.7 

 mm., convexity of brachial valve 14 mm. The dimensions of a detached 

 brachial valve from the typical locality are: length 25.6 mm., width 33 

 mm., length of hinge-line 30 mm., convexity 10 mm. 



Pedicle valve concave in general contour with the surface flattened or 

 slightly convex towards the cardinal extremities and the umbonal region 

 slightly convex over a small area, the greatest concavity near or anterior 

 to the middle ; mesial sinus obsolete ; beak small, pointed, nearly erect, 

 sometimes a little distorted or recurved ; cardinal area of moderate height 

 in the only specimen in which it has been observed, convex from the 

 cardinal margin to the apex with the lower portion sloping posteriorly 

 from the hinge-line at an angle of about 110 degrees, the lateral margins 

 sharply angular, sloping from the beak to the cardinal extremities in 

 slightly flexuous lines due to the distortion of the beak, the delthyrium 

 narrowly triangular, much higher than wide. 



Brachial valve strongly convex, the greatest convexity near or poste- 

 rior to the middle, the umbonal region prominent and usually somewhat 

 protuberant posteriorly beyond the hinge-line, the surface curving more 

 abruptly from the point of greatest convexity to the cardinal margin and 

 a little more gently to the lateral and anterior margins, compressed and 

 somewhat auriculate towards the cardinal extremities; mesial portion of 

 the valve not differentiated ; beak inconspicuous. 



Surface of both valves marked by fine, narrowly rounded or subangular 

 costae, somewhat irregular in size, from two to four occupy the space of 

 one millimeter. Concentric markings of the shell inconspicuous; in no 

 case is the surface of the shell preserved so as to show the minute mark- 

 ings, and the stronger lines of growth are limited to a few more or less in- 

 conspicuous, wrinkle-like markings which are often nearly or quite 

 obsolete. 



Remarks. The types of this species are mostly from the uppermost, mag- 

 nesian limestone layer of the Kinderhook, at Burlington, Iowa, although 

 some examples from the Kinderhook oolite of the same locality are in- 

 cluded in the type lot. The only specimen retaining both valves in artic- 

 ulation is from the magnesian limestone layer and it is from that bed that 

 the most of the specimens in more recent collections have been secured. 

 The specimens most commonly found, both at the type locality and else- 

 where, are detached brachial valves. The only specimen retaining both 

 valves in articulation which has been observed, and the only one in which 

 the length is greater than the width, is one of the types already mentioned, 

 it alone has been the source of the description of the pedicle valve given 

 above ; not enough specimens have been examined to determine whether 

 or not the beak is commonly distorted as in that specimen, or whether 



