762 CAMBRIAN BRACHIOPODA. 



form is much like that of the ventral Talve of Billingsella pumpellyi. It differs from the 

 latter in having, a shorter hinge line in proportion to the width, in the more uniform and 

 stronger convexity of the surface, and in the more elevated apex. 

 The species is named after Dr. Ferdinand von Richthofen. 



Formation anb locality. — Lower Cambrian: (C3) Lower part of the Manto shale [Blackwelder, 1907a, p. 28 

 (list of fossils at bottom of page), and fig. 8a (bed 20), p. 28] 2.5 miles (4 km.) southwest of Yenchuang, Sintai district. 

 Shantung, China. 



A single specimen of a fragmentary ventral valve that may belong to this species occurs 

 in the following locality : 



Lower Cambrian: (C20) Central part of the Manto shale [Blackwelder, 1907a, p. 26 (last list of fossils), and 

 fig. 6 (bed 14), p. 25] on the west side of an isolated butte 1 mile (1.6 km.) south of Changhia, Shantung, China. 



Billingsella romingeri (Barrande). 



Plate XC, figures 2, 2a-n. 



Orthis romingeri Barrande, 1848, Naturw. Abhandl., von Haidinger, Bd. 2, Abth. 1, No. 5, p. 203, PI. XVIII, figs. 

 5a-d. (Described and discussed in German as a new species.) 



Orthis romingeri Barrande, 1879, Syst^me silurien du centre de la Bohgme, vol. 5, pt. 1, PL LXII, figs, ii: 1-4. 

 (Figs. 3a, 3c, 3b, 3d, and 3e are copied in this monograph, PL XC, figs. 2, 2a-d, respectively.) 



Orthis romingeri Barrande, Pompeckj, 1896, Jahrb. K.-k. geol. Reichsanstalt, Bd. 45, Hft. 3, pp. 513-514, PL XV, 

 figs. l-5a. (Described and discussed in German.) , 



Billingsella romingeri (Barrande), Walcott, 1905, Proc. IT. S. Nat. Mus., vol. 28, pp. 243-244. (Described and dis- 

 cussed as below.) 



Shell transverse, the general outline being irregularly subquadrate to subsemicircular. On 

 the ventral valve the cardinal line slopes toward the beak at a low angle, while in the dorsal 

 valve it is approximately straight. In some shells the greatest width is at the hinge line, wliile 

 in others it is about the middle of the valve. There is considerable variation in length and 

 breadth, as may be seen by comparing the figures illustrating this species. 



The ventral valve is rather strongly convex and the dorsal valve moderately so. The 

 dorsal valve is slightly flattened from the umbo to the frontal margin, the flattening sometimes 

 taking the form of a shallow depression. A low, broad mesial sinus occurs on the dorsal valve 

 and is strongly marked in the young shells. The surface is marked by roimded, bifurcating, 

 radiating costse crossed by concentric lines of growth and undulating concentric strise. The 

 radiating costse varj^ in size and character in specimens from the same locality. In some 

 specimens they are very regular, while in others there will be wider interspaces or a variation 

 in the manner of interpolation. The ridges of growth also vary in strength and elevation in 

 dift'erent shells. 



The largest shell in a considerable quantity of material has a length in the ventral valve of 

 13 mm. and in the dorsal valve of 10 mm., \vith a Av-idth of 15 mm. Cardinal area of ventral 

 valve rather high and slightly incmwed. It is marked by transverse strise of growth that cross it 

 parallel to its base; the plane of the area extends backward at an angle of about 10° to the plane 

 of the margin of the shell; the delthj^rium is rather large; a deltidium is indicated in some of 

 the casts, but none of the specimens show it clearly. The cardinal area of the dorsal valve is 

 about one-half the length of that of the ventral valve; it extends backward at an angle of more 

 than 45° to the plane of the margin of the valve and is divided midway by a strong delthyrium 

 which is covered, for a part of its distance at least, by a convex chilidium. 



The traces of the vascular system in the ventral valves are seen in the main vascular trunks, 

 which extend well forward toward the front margin, where they appear to bifurcate, the inner 

 branch extending toward the median line and the lateral branches apparently connecting with 

 the peripheral canal that arches backward about the ovarian areas between it and the main 

 vascular trunks. No points of attachment of the various muscles in the ventral valve have 

 been observed. The area in which the diductor muscles are attached is well marked in Plate 

 XC, figures 2h and 2i, and the cardinal process of the dorsal valve in figures 2j and 2k. There 



