142 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 53 



TABI^E OF CLASSIFICATION. 



r r 



Rustellidse 



= \ 



Pateriiiidje 



Curticiidae 



f OboHnce 



X 



< 



I ^ 

 O 



Elkaniinse 



Xeobolince 



a r 



2 I Kutorgniidce 

 ■& -i 

 £ Schuchertinidse 



r r 



Mickwitzia 



Micromitra 

 (Paterina) 

 (Iphidella) 



Volborihia 



(?)Helmersenia 



Obohis 



(Brofiseria) 



(PaUeobohis) 



(Fordiiiia) 



(Lingulobolus) 



(Mickwitzella) 



( Acritis) 



(Schmidtia) 



(Westonia) 



Litigulella 

 (Leptenibolon) 

 (Liugulepis) 



Del^adella 



Elkania 

 Neobolus 



Bicia 

 Dicellonius 



Obolellidce 



o ■! 



Siphonotretidse 



Acrothelinfe 



t ^ 



Acrotretiiise 



I I 



Discinida; 



Q I 



f 



.S -{ Craniidce 



Billing 

 Unas 



Kutorj;iiia 



Schiichertina 



;el- 



Eoorthince 



Rafiiies- 

 quinse 



6g r OK f 



aa ! aS ! 

 o = i o = i 



cs r 



CO 



p -! Svutrophiidic 



I ■ 



f Oholella 

 I (Glyptias) 

 -i Botsfordia 

 I Schizopholis 

 L (?)Quebecia 



f Yorkia 

 Dearbornia 

 Trematobolus 

 I Schizainboii 

 ] Siphoiiotreta 

 [ Kej'serlingia 



( Acrothele 

 < (Redlichella) 

 [ Di.-ciiiolepis 



f Linnarssouella 

 j Acrotreta 

 I Acrothyra 

 L Disciuupsis 



< Orbiculoidea 



Philhedra 



f Nisusia 

 ] (Jamesella) 

 ', Protorthis 

 L (Lcperia) 



f Winiaiiella 

 Billingsella 

 ■J Orusia 

 1 Otusia 

 L Wynnia 



/ Eoorthis 



I Finkehiburgia 



Eo.strophoniena 



f (?)Swaiitonia 

 I Syiitrophia 

 I Huenella 

 t Clarkella 



Order ATREMATA Beecher, 1891 (emend) 



Primitive inarticulate, corneous or calcareo-phosphatic Brachio- 

 poda with the pedicle emerg-ing more or less freely between the two 

 valves. Growth takes place in general around the anterior and 

 lateral margins. Specialized forms show tendency to develop rudi- 

 mentary articulation. Delthyrium originally unmodified, in later 

 genera modified by pseudodeltidia and pseudochilidia, or by thick- 



