158 PROCEEDINGS OF THE NATIONAL MUSEUM. 



care in descriminating between them. B. gregarla is proportionally 

 higher, the anterior end especially being wider. The lobing of the 

 valves seems to be rather more variable in the Kansas .species, while 

 no mention of the antero-dorsal spine is to be found in descriptions of 

 B.? iU'ciiata. 



F</rvMtion and locality. — Extremely abundant on ))edding planes 

 of clavey limestone bands of the Upper Car])oniferous at Kansas City. 

 Missouri. * 



IIoloty2)e.—OAi. No. 3.5625, U.S.N.M. 



BEYRICHIELLA BOLLIAFORMIS, new species. 

 Plate XI, %s. 7, 8. 



Length 0.87 nun., height 0.52 mm., thickness 0.35 nmi. 



Carapace rather elongate subovate, the posterior end wider and more 

 oblique than the anterior; cardinal angles obtuse; ends nearly equal 

 in thickness. Surface of valves with two rounded and not very promi- 

 nent nodes, subcentrally situated, one on either side of the deep median 

 sulcus; nodes generally connected by a more or less o))scure loop; pos- 

 terior node rather better defined though smaller than the anterior. 

 Ventral part of valves swollen without being detinitely ridge-like. 

 Dorsum channeled; ends and ventral edge, especially of the left valve, 

 distinctly rimmed. Ventral edge of left valve overlapping that of the 

 right. 



The two nodes with the connecting loop impart an appearance 

 strongly suggestive of certain species of Boll i a. The "" loop " is some- 

 times well defined, but in other examples it is scarceh' distinguishable. 

 The species evidently is closely related to Beyrichia fodicata Jones and 

 Kirkby and B. faMlgiata Jones and Kirkby, but its valves are rela- 

 tivel}^ shorter and margined b}^ a distinct rim, a feature not observed 

 on the British species. 



Formation and locaJity. — Cottonwood shales, 2 miles east of Cotton- 

 wood Falls, Kansas. The same species occurs in the Upper Carbon- 

 iferous deposits in Baylor and other counties in north central Texas. 



Holotype.—C2ii. No. 35631, U.S.N.M. 



BEYRICHIELLA BOLLIAFORMIS TUMIDA, new variety 

 Plate XI, tigs. 9 to 11. 



The form which it is proposed to designate provisionally as above 

 differs from the typical varietj^ of the species in two particulars, (1) 

 the outline is somewhat rhomboidal, the anterior border being o])lique, 

 beginning to curve backward just beneath the antero-dorsal angle, and 

 (2) the anterior third of the valve within the rim is much more tumid, 

 this portion of the carapace being indeed decidedly thicker than the 

 posterior part and generally exceeds even the middle thickness. Oc- 

 casionally, as shown in tig. 10, the antero median node is obsolete. 



