no. 1046. REVISION OF BEYRICHIIDM—VLRICH AND BASSLER. 283 



Finally, the posterior location of the peculiar ventral pouch that 

 Reuter and others have interpreted, we believe correctly, as ovarian 

 inflations, is wholly in accord with the other criteria. 



BEYRICHIA OF AUTHORS. 



The genus Beyrichia was founded by McCoy in 1846.° His " rough 

 -ketch " of the valves of the Irish species that first convinced McCoy 

 that these fossils were bivalved Crustacea and not trilobites gives a 

 crude idea of the common Silurian form subsequently identified by 

 Jones and others with B. klcedeni McCoy. As McCoy ranks "Battus 

 tuberculatus " of Kloeden as a synonym of his Beyrichia klcedeni. and 

 as the two forms are distinguishable species, it is difficult to decide 

 which of the two should rank as the genotype. However, as they are 

 unquestionably congeneric, the point is of little consequence. 



Subsequent authors have referred a considerable variety of Ostra- 

 coda to the genus. In fact, for many years it served as the temporary 

 lodging place for nearly all of the Paleozoic species with furrowed or 

 ridged valves. As noted above, a 

 large part of these has been re- 

 moved and distributed among other 

 genera, but at the present writing no 

 less than 150 species and varieties 

 are still credited to Beyrichia. 

 Many of these remaining species are 



not strictlv congeneric with the type „ ., ., „ , 



° t J l Fig. 11. — < "TV of McCoy's obiginal 



and hence will be removed, chiefly sketches of Beyrichia klcedeni. 



to new genera and to the long mis- 

 understood Klaedenia, the other more obvious departures from the 

 generic type having been already mostly weeded out through the 

 efforts of Jones, Holl, Kirkby, Krause, and Ulrich. 



The genus Klcedenia constitutes a close ally of the typical Bey- 

 richise. The practical discrimination of the two groups, in certain 

 cases at least, suggests that the boundary is artificial and probably 

 results in occasional unnatural associations. But it is impossible to 

 wholly escape this condition in any classification that is not too in- 

 volved to be practical. Therefore, since the distinctive characters 

 relied on in separating the two groups operate, as a rule, in apparent 

 accord with genetic lines, Klcedenia is accepted, with some justifiable 

 modifications of the original diagnosis, as a useful designation. The 

 comparatively few species about which there is doubt are provision- 

 ally left with Beyrichia. 



Accepting Beyrichia klcedeni and B. tuberculata as the types of the 

 genus, and bearing in mind the ground to be occupied by the revised 

 Klmdenia, the restricted genus Beyrichia may be defined as follows: 



°Syn. Sil. Foss. Ireland, p. 57. 



