no. 1C46. REVISION OF BEYRICHIIDJB—ULRICH AND BAS&LER. 291 



of the valve in 0. tumida, and having learned that this is invariably 

 situated behind the middle, no other course remained than to interpret 

 the bulbous end as anterior. 



Having oriented the valves in this manner, the relations of C. 

 tumida to Drepanella richardsoni became fairly clear: but even then 

 it required a more perfect specimen than the original types to enforce 

 conviction. This specimen, recently collected at Moreland, Ken- 

 tucky, has a thick marginal ridge running from the post-dorsal angle 

 to the middle of the ventral v^l^v, where its further extent is lost in 

 the ventral slope of the anterior bull). But its anterior extremity 

 reappears on the opposite side of the bulb as a distinct node. Taking 

 essentials alone into account, the characters of ('. tumida are not 

 greatly different from those of Beyrichia like B. protuberans, B. 



17 



18 



f9 



20 



21 



22 



Figs. 17—22.— 17. Right valve of Drepanella macra Uleich for comparison with 

 pig. 20. Left valve of Beyrichia tuberculata (Klosden). is. Bight valve of 

 Drepaxella crassinoda Ulrich for comparison with left valve of Beyukhia 



NOETLINGl BEDTER (lie;. 121). 1!). LEFT VALVE OF DREPANELLA NITIDA (ULRICH) FOR 

 COMPARISON WITH THi: CORRESPONDING VALVE OF BEYRICHIA BADERI REUTERj SHOWN 



in fig. 22. (Copied after TTlrich and Reuter.) 



jonesi, or B. clavata, in which also the anterior lobe is the most prom- 

 inent part of the valves and the posterior lobe extends forward be- 

 neath the middle and anterior lobes. Therefore, despite the rather 

 strong dissimilarity in aspect, there seems really to be no very essen- 

 tial difference between ('. tumida and Beyrichia. The posterior half 

 is nearly the same in both, and only the great development of the an- 

 terior lobe gives the Ordovician species a strange look. However, as 

 the writers are convinced that the latter is related genetically to un- 

 questionable species of Beyrichia, and that the differences noted are 

 not of greater importance than those obtaining between, for instance, 

 the B. tuberculata and the B. l-lo'deni groups, the species tumida is 

 removed from Ctenobolbina, where it certainly does not belong, to 

 Beyrichia. 



