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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXV. 



Isochilina, and the ridge even is represented in subdued form in /. sub- 

 nodosa. The significant fact in this connection is that in this, we 

 might almost say prophetic species, the above discussed criteria by 



10 



Figs. 1-10. — 1. Left side of entiee specimen < u of Lepebditia fabulites (Conbad). 

 Anterior end indicated by the small "oculab" tubercle, its lessee height, 



and backward swim; of valve. -. left valve of isochilina ? subn sa ulbich, 



x ?>, a nearly equal form. anterior side indicated by ocular and other tuber- 

 cles, that when present are always in front half of valves. .'!. right valve 

 of isochilina? clavigeba (beybichia clavigera jones) x 10, showing the ocu- 

 lar tubercle and muscle spot of lepekditi idje, thus determining which is the 

 anterior side and incidentally affording a good example of betbal swing. ob- 

 dovician it'hazy shale), near ottawa, canada. 4. left valve < >f beyrichia tu- 



BEBCCLATA I KliEDUN I X 5 CUTER EEUTEE). ANTEBIOB SIDE RECOGNIZED BY ITS INFE- 

 RIOR HEIGHT, SLIGHT EETBAL SWING. AND BY CORRELATION < iF NODES "F VALVE. 5. RIGHT 

 VALVE OF BEYBICHIA CLAVATA KOLMODIN (AFTER KlESOW). ORIENTATION DETERMINED 

 BY SAME CRITERIA AS IN FIGURE 4. 6. LEFT VALVE OF CTENOBOLBINA ALATA ULBICH, 

 X I s (AFTER DLBICH). ANTERIOR END BECOGNIZED BY ITS TAPEB AND BY THE BETBAL 

 SWING OF THE OUTLINE. 7. LEFT VALVE OF CTENOBOLBINA CILIATA lEMMONS), > 18 

 (AFTER CJLEICH). OBIENTATION DETEBMINED BY COMPABISON OF LOBES WITH THOSE OF 

 C. ALATA, IN WHICH THE ANTEBIOB END IS NARROWER AND THE RETRAL SWING MORE PBO- 

 NOUNCED. 8. BEYBICHIA (STEUSLOFFIA) LINNABSSONI (KBADSE). RIGHT VALVE, > 15 



(after redteb). obiented bv compabison of lobes with those of beybichia cla- 

 \ata and b. tubebculata. '.'. beybichia saltebiana jones, x 10 i after reuteri. 

 The ends being almosi exactly local in this species the obientation of its 

 valves is possible only by compabison of its lobes with those of other bey- 

 rdhi.e, like b. clavata. in these, other cobbobobative criteria are available, 

 si i ii as the taper of the valves antebiobly and the retral swing of the out- 

 line, accordingly the figube bepbesents a right valve. 10. different view's of 

 a left valve of beybichia tubebculata-buchiana reuteb, xg (after reuter). 

 The example figubed possesses the ventral pouch, which feature Reuter and 

 other writers regard as distinguishing the female in beybichia and allied 

 genera. the pouch is located invariably on the lower pabt of the posterior 



LORE. 



which the right valve is distinguished from the left is supported by 



tiio evidence of the eve-tubercle. 



