144 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



pletely restrict the pedicle opening to the ventral valve. The radicle 

 of the Trimerellidae, by way of the Neobolinae, appears to be in this 

 subfamily in the thick-shelled Middle Cambrian forms of O bolus 

 <s. s.) 



Obolus 



(Broggeria) 



(Palceobolus) 



(Fordinia) 



(Lingidobolus) 



{Mickwitzella) 



(Acritis) 



(Schmidtia) 



{W estonia) 

 Lingulella 



(Leptembolon) 



(Lingulepis) 

 Pel gad el la 



Subfamily ELKANIINiE Walcott and Schuchert, new 



Divergent Obolidse with posterior or marginal (not central) plat- 

 forms, to which are attached the central and outside and middle 

 lateral muscles. 

 Elkania 



Subfamily NEOBOLIN^ Walcott and Schuchert, new 



Progressive Obolidse with posterior platforms, to which were 

 probably attached the central and outside and middle lateral muscles. 

 Subfamily apparently progressive from the Obolinse to the Trimerel- 

 lidae, though the platform is posterior and not subcentral as in the 

 Trimerelloids. 



Neobolus 



Subfamily BICIIN/E Walcott and Schuchert, new 



Progressive Obolidse with the pedicle restricted to the ventral 

 valve and more or less enclosed by a pedicle tube, and with rudi- 

 mentary articulation. The transgressing stock from the Atremata 

 to the Neotremata (Obolellidse). 



Bicia 



Dicellomus 



Superfamily KUTORGINACEA Walcott and Schuchert, new 



Progressive, thick-shelled, almost calcareous Atrematous-like 

 shells, tending to be transverse and developing rudimentary articula- 

 tion, more or less rudimentary cardinal areas, pseudodeltidia, and 



