392 CAMBRIAN BRACHIOPODA. 



seen between the two. In the dorsal valve the umbonal scar is very close to the area and 

 extends some distance on each side of the median line. It is marked by fine striae subparallel 

 to the longitudinal axis of the shell. In one cast (PL XII, fig. lb) the position of the trans- 

 median and anterior lateral scars is indicated; also the area in which the central, middle, and 

 outside lateral scars occur, but the scars are not differentiated. In the dorsal valve (PI. XII, 

 fig. le) the central (h) and anterior lateral (j) scars are clearly defined also the position of the 

 transmedians (i). 



Portions of the markings left on the shell by the vascular system are well preserved in a 

 few specimens. The description is of the cast, or as the markings are shown on the thin inner 

 layer. The main sinuses are slightly rounded ridges that arch from the beak outward toward 

 the center and then inward well toward the anterior margin. Those of the ventral valve are 

 shown in Plate XII, figures lb,lc,and ld,and the dorsal in figure le. The interior lateral branches 

 in the ventral valve extend transversely from the main sinus nearly to the median line, except 

 toward the front, where they arch sUghtly backward (PL XII, fig. Ic); the exterior lateral 

 branches arch forward to the edge of the depressed rim, where they appear to pass into the small 

 interosculating canals that cross the rim to the outer margin, each canal dividing into three or 

 more branches; the peripheral vascular canal of Mickwitz [1896, p. 97] does not appear on any 

 of the specimens available for study, but this may be owing to our not having the inner surface 

 of the inner layer to examine. 



The parietal scar is distinctly shown in front of the visceral cavity in both valves, but it 

 has not been traced outside of the main sinus, although the positions of the transmedian and 

 anterior lateral scars in the dorsal valve (PL XII, fig. lb) indicate its approximate lateral 

 extension. 



Observations. — This large fine species is extensively illustrated by Barrande, but the material 

 at his command evidently did not satisfactorily show the muscle scars and vascular markings 

 of the interior of the valves. One figure of the ventral valve [1879b, pi. CVI, fig. iv: 4] indi- 

 cates the relative position of the main vascular canals and muscle scars (copied on PL XII, 

 fig. Id, of this monograph), but it was not sufficiently clear to convince Mickwitz [1896, pp. 19-20] 

 that the species should be referred to Oholus, and Hall and Clarke [1892c, pp. 68-69] sug- 

 gested that it might be an Obolella. 1 found in the collections of the Museum of Comparative 

 Zoology at Cambridge a number of specimens showing casts of the interior of both valves. Of 

 these, three are figured in this monograph (PL XII, figs, lb, Ic, le, 9, and 9a). Plate XII, 

 figure Ic, is of a specimen preserving the tliin inner layer, on the exterior of which vascular 

 markings are beautifully preserved. Owing to the coarse character of the sandstone matrix, 

 the interior casts preserve only traces of the main sinuses. Figure le represents a similar 

 specimen in which the exterior lateral branches of the main sinus appear to subdivide at the 

 inner edge of the flattened rim and to continue across the rim to the outer edge, inosculating 

 and bifurcatmg in an irregular manner. 



This is one of the most recent as well as the largest species of the genus. In form and the 

 arrangement of the vascular markings and muscle scars it may be compared with 0. matinalis 

 (Hall), which, however, is a much smaller species from the Middle Cambrian fauna. In outline, 

 size, and general arrangement of the muscle scars and visceral cavity the species may be com- 

 pared with Oholus {Linguloholus) affinis (Billings) (PL XVI, figs. 1, la-e). 



The specific name was given in honor of K. Feistmantel. 

 Formation and locality. — Lower Ordovician: (303i [Barrande, J.879b, PL CX]) Sandstone of Stage dl, at Kruschna 

 Hora; and (303] [Barrande, 1879b, PI. CVI]) Etage dl, at Czerhowitz; both in Bohemia, Austria-Hungary. 



Oboltjs fragilis (Walcott). 



Plate XXIII, figures 5, 5a-e. 



Obelus (Lingulella) fragilis Walcott, 1898, Proc. U. S. Nat. Mua., vol. 21, p. 404. (Described and discussed essentially 

 as below as a new species.) 



General form ovate, with the ventral valve subacuminate and dorsal valve broad ovate; 

 valves apparently moderately convex, as determined from the specimens more or less com- 

 pressed in the shale. Surface of shell marked by concentric lines of growth, and what appears 



