CLASSIFICATION CAMBRIAN BRACHIOPODA — WALCOTT I43 



ened, striated, and more or less furrowed or even cleft vertical car- 

 dinal margins, the ventral cleft in most specialized forms tending to 

 enclose the pedicle and finally restrict it to the ventral valve; when 

 completely so the genera are referred to the order Neotremata. 



Superfamily RUSTELLACEA Walcott, new 



Primitive, thick-shelled, corneous or calcareo-phosphatic Atremata 

 developing more or less of pseudodeltidia and pseudochilidia. 



Family RUSTELLID^ Walcott, new 



Primitive Rustellacea with the delthyrium small, open, and not 

 much modified by pseudodeltidia or pseudochilidia. Muscle scars 

 and vascular sinuses not well defined in the shell. 

 Rustella 



Family PATERINID^ Schuchert, 1893 (emend) 



Progressive Rustellacea with the delthyrium more or less closed 

 by pseudodeltidia or pseudochilidia. 

 Mickwitaia 

 Micromitra 



(Patcrina) 

 (Iphidella) 

 Volhorthia 

 (?) Helmersenia 



Superfamily OBOLACEA Schuchert, 1896 (emend) 



Derived (in Rustellacea), progressive, thick-shelled, calcareo- 

 phosphatic or corneous Atremata without pseudodeltidia and pseudo- 

 chilidia. Rounded or linguloid in outline, more or less lens-shaped 

 and fixed by a short pedicle throughout life to extraneous objects. 



Family CURTICIID^ Walcott and Schuchert, new 



Primitive Obolacea with a high, well-defined delthyrium. Interior 

 characters much as in Obolidas. 

 Curticia 



Family OBOLID^ King, 1846 (emend) 



Derived, progressive Obolacea with thickened, striated, vertical 

 cardinal areas traversed by pedicle grooves. Muscles and vascular 

 trunks strongly impressed in the valves. 



Subfamily OBOLIN.^ Ball, 1870 (emend) 



Primitive Obolidae with the pedicle grooves more or less shallow 

 or deeply rounded, but never tending to form a sheath or to com- 



