NO. 1395. CA MBRIA N BRA OHIO POD A— WA L CO TT. 243 



Foriuaflo)) (ind Jocrillfi/. — Middle Cambrian. Chang H.sia liniestonc. 

 Two and one-half miles south of Yen Chuang, Shantung-, China. 



Collection of Mr. Eliot Blackwelder, Carnegie Institution P]xpedi- 

 tion to China. 



BILLINGSELLA ROMINGERI Barr. 



Orthh romingeriBARR, Ueber die Brachiopoden der Sil. Schi. Bohmen, II, Abth. 



Haidingers Naturw. Abhandl., II, 1848, pp. 203, pi. xvii, fig. 8. 

 Orthis romingeri Barr, Syst. 811. BiJheme., V, 1879, pi. lxii, figs. 1-4. 

 fhihis romingeri Pompeck.i, Die Fauna des Cambrium von Tejfovic und Skrej in 



Bohmen, Jahrbuch der k. k. geolog. Reichsanstalt, 1895, XLV, 1896, Pts. 



2 and 3, pp. 513, pi. xv, figs. l-5a. 



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 approxi- 

 mately straight. In some shells the greatest width is at the hinge 

 line, while in others it is about the middle of the valve. There is con- 

 siderable variation in length and breadth. 



The ventral valve is rather strongly convex and the dorsal valve 

 moderately so. The dorsal valve is slightl}^ flattened from the umbo to 

 the frontal margin, the flattening sometimes taking the form of a shal- 

 low depression. A low, })road, mesial sinus occurs on the dorsal valve 

 that is strongly marked in the young shells. The surface is marked 

 by rounded, bifurcating, radiating costse, crossed bj^ concentric lines of 

 growth and undulating concentric striae. The radiating costse vary in 

 size and character in specimens from the same locality. In some speci- 

 mens they are very regular, while in others there will be wider inter- 

 spaces or a variation in the manner of interpolation. The ridges of 

 growth also vary in strength and elevation in diflerent shells. 



The largest shell in quite a large quantity of material has a height 

 in the ventral valve of 13 mm. and in the dorsal valve of 10 mm., with 

 a width of 15 mm. Cardinal area of ventral valve rather high and 

 slightly incurved; it is marked by transverse stria? 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 

 delthyrium 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 delthy- 

 rium, 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 api)arently connect- 



