no. 1646. REVISION OF BEYRICHIID&— ULRICH AND BASSLER. 325 



Jones and Kirkby), all from the Carboniferous rocks of Great 

 Britain, and •/. bottiaformis and var. tumida {Beyrichiella Ulrich 

 and Bassler), 6 and J. gregaria {Beyrichiella Ulrich and Bassler) c 

 from rocksof Pennsylvanian age in Kansas and Texas. Other Ameri- 

 can species are known, but remain to be described. 



Jonesina sometimes resembles Klmdenella to a marked degree. 

 This is true especially of ./. craterigera, but with entire specimens the 

 observer should experience little difficulty in distinguishing them, the 

 matter of relative size of the valves being reversed in the two genera. 

 In the older genus the right valve is the larger, whereas in Jonesina 

 it is the left. 



In correlating the nodes of Jonesina with those of a typical Bey- 

 richia, it is to be observed that the median lobe of the latter corre- 

 sponds to the post-median node of Jonesina, the one, two, or three 

 nodes in front of the median sulcus being equivalent to the single or 

 dissected anterior lobe of Beyrichia. Obviously the location of the 

 homologous parts in the two genera is widely different. 



"Ann. and Mag. Nat. Hist. (5), XVII, 1SS6, p. 258, pi. vin. figs. 4-6. 

 h Proe. U. S. Nat. Mus., XXX, 1906, p. 158, pJ. xi, figs. 7-11. 

 c Idem., fig. IS. 



