298 



PR<x'i:i:i)i\<;s of the xatioxal mi seiw. 



VOL. XXXV. 



sible that the figure given by Krause is a little defective at the base 

 of the median and posterior lobes. The Waldron species sometimes 

 even exhibits a suggestion of the V-shaped crest, but, as is shown on 

 Plate XXXVII, the ventral part of the posterior lobe is distinctly 

 contracted, giving an appearance quite different from the same part 

 in Krause's figure of B. reticulata, but closely simulating the fringed 

 species of the B. maccoyiana group. 



As figured, B, reticulata appears to be somewhat obscurely lobed, 

 which, with the broad frill, is somewhat suggestive of Ei<nj<-litl'tna. 

 But it has no sharply defined median pit, and it is thought unlikely 

 that the marginal frill is hollow T ed out on its inner surface. The 

 median lobe also is too long. It seems probable, therefore, that the 

 general resemblance to Eurychilina does not indicate close genetic 

 relations. 



The J!, linnarssoni group has a sufficiently uniform expression to 

 suggest the advisability of its separation as an independent though 

 decidedly synthetic genus. The crested valves recall Strepula, the 



Figs. 45— 40. — Right valve of Beyrichia reticulata (Krause), X 20, and the same 

 valve op Eurychilina reticulata Ulrich, 20 (after Ulrich)-, showingi the 



similarity of THE TWO forms referred To in tiii: TEXT. 



mode of lobation is very much as in the Beyrichia salteriana group, 

 and through this resembles on the one hand the typical Beyrichian 

 section of B. tuberculata and on the other Klmdenia. In still an- 

 other direction, close alliance with Ctenobolbina, as above outlined. 

 is established. If Ctenobolbina wore expanded to take in a part of the 

 group, consistency would demand that species of the />. salteriana 

 group be also included. But this would render the boundary between 

 Ctenobolbina and Beyrichia more artificial than it is desired to make 

 it. Besides, it would split up an apparently very natural association 

 id' species. 



The group as a whole is undoubtedly more in accord Avifh Bey- 

 richia than Ctenobolbina, and in the first suggestion of the hetero- 

 geneous mas- of Beyrichiidse, ifs species were left with or referred to 

 the restricted genus without much hesitation. However, in the still 

 considerable and variable mass of species having the essential charac- 

 ters of Beyrichia, the comparative entity of the B. linnarssoni group 

 is lo>t sight of. In order to secure its deserved recognition without 



