BRACHIOPODA OF THE MAEL BEDS. 7 



to the axis of the valves. Lateral margins of tlie beak, angular. Center 

 of the valve toward the front usually flattened or concave, and the lateral 

 slopes impressed. Dorsal valve nnich less deep than the ventral; the 

 beak small and invariably incurved within the deltidial opening of the 

 ventral in half-grown or mature specimens ; front and anterior surface of 

 the valve flattened or concave, leaving an angular ridge dividing the cen- 

 tral area from the lateral slopes. This latter feature is frequently exag- 

 gerated to so great an extent as to give a decidedly plicate appearance 

 to the front half of the shell. Shell-surface marked by numerous lines 

 of growth, often grouped so as to form varices of growth toward the front 

 in old specimens. Shell-substance finely punctate, the punctse usually 

 visible under a hand-magnifier of moderate power ; more distinctly seen, 

 however, on exfoliated surfaces. In the interior the crura are slender near 

 their junction with the dorsal valve, but rapidly expand into a broad loop 

 of from three to five eighths of an inch in length and more than two-thirds 

 as great a width, and very angular at the bendings. There have been two 

 varieties of this species described under distinct names, T. ovalis and T. 

 fragilis, Morton. There may be some reason for regarding the latter as a 

 good species, as it occurs in beds where the other form is scarcely or not at 

 all represented This is, I believe, notably the case at Harrisonville, New 

 Jersey. The characters of these varieties are separately noted below. 



Variety /ra^'i/is, rr Terehratula fragilis Morton, PI. I, Figs. 15-18. This 

 form is common enough at nearly all localities where the species occurs. 

 It is found of all sizes, from a little more than an inch in leng'th to 

 those nearly as large as the normal form of the species. It is usually, how- 

 ever, smaller in size, more cylindrical, and very strongly plicated ; the jilica- 

 tions frequently forming strong lobes and extending to within half an inch 

 or so of the beak on the dorsal valve and nearly as far on the ventral. I 

 can find no feature which will serve to distinguish this form from the normal 

 type of T. Harlani constant enough to be relied upon. Tlie thinness of the 

 shell is no greater than that of the generality of those of the other form. 

 There is a decided and marked difference in the size and character of tlie 

 punctse of the shell observable in some individuals of this variety, the 

 pores being smaller and much more densely crowded together, forming 



