no. 1646. REVISION OF BEYRICHIID2E— ULRICH AND BASSLER. 323 



second species of Beyrichiella. A third, the only known species from 

 American strata, was described by Ulrich as Ulrichia confhtens. 

 Viewed in the narrow sense in which this genus was proposed and in 

 which it is now thought desirable to recognize it, Beyrichiella is 

 clearly distinguished from other members of the subfamily. The 

 shell is relatively longer than that of Kirkbyina and its larger valve 

 is not the right as in that genus, but the left. The lobation of the 

 valves is also less simple, the low ventral ridge, connecting the two 

 larger lobes, being a character not observed in Kirkbyina. The gen- 

 eral shape of the carapace is decidedly like that of B eyrie Mop sis, but 

 the characteristic rounded, median — or rather post-median — node of 

 that genus is wanting in Beyrichiella. 



Genus BEYRICHIOPSIS Jones and Kirkby. 



Beyrichiopsis Jones and Kirkby, Geol. Mag., Dec. 3, III, 1886, ]». 434: Proc. 



Geol. Assoc, IX, 1880, p. 500: Quart. Journ. Geol. Sot-. London, XLII, 



1886, p. 506. 

 Beyrichiopsis Ulrich and Bassler, Proc. XL S. Nat. Mus., XXX, 1900, p. 



152. 



Carapace small, about 1 mm. in length, oblong, sub-quadrate to sub- 

 elliptical, straight on the dorsal side, tapering slightly and thickest 

 anteriorly; on the whole, rather strongly convex. A broad based, 

 rounded swelling or lobe occupies the greater part of the anterior 

 half. A second, smaller rounded eminence occurs behind the mid- 

 dle and usually above the mid-height of the valve. It is often sur- 

 rounded by a slight depression usually deepest on the anterior side. 

 Free edges of valves usually with a broad, spiny frill ; in other cases 

 merely denticulate. Two or three thin, crest-like ribs commonly 

 cross the surface in a longitudinal direction. 



Genotype. — Beyrichiopsis fimbriata Jones and Kirkby. Other 

 typical species are B. comuta, B. svbdentata, B. fortis, B. granulata, 

 and B. simplex, all described by Jones and Kirkby from British 

 Carboniferous specimens. Two new species in the Ulrich collection 

 in the U. S. National Museum were collected from the basal shales of 

 the Tullahoma formation in central Tennessee. One of these has 

 a frill like B. -fimbriata, the other is more like B. comuta. 



Compared with the other genera of the subfamily Kloeclenellinpe, 

 Beyrichiopsis is distinguished at once by the small, rounded post- 

 median node. Otherwise the genus is not greatly different from 

 Beyrichiella, its nearest ally, the usual presence of a spiny marginal 

 frill being of subordinate importance. Another difference, how- 

 ever, is found in the transverse ventral ridge seen in Beyrichiella but 

 which is absent in Beyrichiopsis. 



a Geol. Mag., Dec. 3, III, 1880, pp. 434-437. 



