no. 1046. REVISION OF BEYRICHIID2E— ULRICH AND BASSLER. 3Q7 



Tetradella quadrilirata a (Beyrichia quadrilirata Hall and Whitfield). 

 Tetradella (KiesovHa) radians (Beyrichia radians Krause). 

 Tetradella Hbeiriand (Beyrichia ribeiriana Jones). 

 Tetradella simplex (Tetradella quadrilirata var. simpler Ulrich). 

 Tetradella subquadrans a Ulrich. 



In the original description of the genus'' the species subsequently 

 distinguished as Ceratopsis c were included. In 1889 d the typical 

 species was erroneously referred to Strepula Jones and Holl. In 

 1894, e when the revised description of Tetradella was published, cer- 

 tain European species were referred to the genus, which it is now 

 thought advisable to view as doubtful or to place elsewhere. Thus, 

 T. signata Krause, as mentioned on page 295, is now referred to 

 Stexslofjia, a proposed subgenus of Beyrichia. T. {Beyrichia) er- 

 ratica Krause may belong to the same subgenus, but it is preferred 

 to regard it provisionally as questionable, because, with the evidence 

 available to the writers, it is impossible to decide that it is not a 

 Strepula rather than a Tetradella or a Steasloffia. T. {Beyrichia) 

 lacunata Jones may be a degenerated species of the genus, but in the 

 absence of satisfactory specimens it should be placed as doubtful. 

 T. {Beyrichia) afp'nis Jones also is doubtful, and the same is true of 

 T. {Beyrichia) digitata Krause. Of the species there designated as 

 " somewhat doubtful upper Silurian representatives," B. nodulosa is 

 returned to Beyrichia, but B. dissecta Krause, B. radians Kiesow, and 

 B. inamillosa Krause must be removed or continue to be regarded as 

 questionable. The dissection of the lobes in the latter two is some- 

 what similar to what occurs in Beyrichia of the group of B. tubercu- 

 lata (see page 289). Critically compared, however, the breaking up 

 of the lobes is not exactly the same. No Tetradella coidd be dissected 

 so as to look like B. tuberculata or any of its immediate allies; but 

 if the vertical part of the ridges of, say, Tetradella subquadrata, were 

 divided transversely and the furrows were extended ventrally through 

 the marginal ridge, the result would be, in every essential respect, 

 precisely as in B. dissecta. The size of the valves also accords much 

 better with the average for Tetradella than for Beyrichia. Under 

 the circumstances, a separation from both Beyrichia and Tetradella 

 is suggested, but should it be decided, as the writers believe, that the 

 two species were derived from Tetradella. the demands of classifica- 

 tion might very well be satisfied by subgeneric discrimination. The 

 name Kiesowia is proposed, with Beyrichia dissecta Krause as the 

 type of the new genus or subgenus. 



" American species. 



6 Jour. Cincinnati Sec Nat. Hist.. XII 1. 1890, p. 112. 



'' I'lrich, Geol. and Nat. Hist Surv. Minnesota, Final Kept-. HI. l'l. :.'. 1894, 

 p. <>75. 



d Ulrich, Geol. Surv. Canada, Cont. Micro-Pal., Pt. -, 1889, p. 54. 



' 1'lrich. Geol. and Nat. Hist. Surv. Minnesota, Final Rept., III. l'l. •_'. 1894, 

 p. <!77. 



