370 



MOLLUSCOIDEA 



THYLUM V 



liustella Walcott (Fig. 542). The most primitive known Brachiopod. 

 Lower Cambrian ; Vermont. 



Family 2. Paterinidae Schuchert. 



Progressive Rustellacea with the pedide aperture more or less closed hj 

 homoeodeltidia and pseudochilidia. Cambrian. 



Paterina Beecher (Fig. 543). Surface concentrically ornamented. 



Fig. 542. 



Rustella edsoni Walcott. Lower Cam- 

 brian ; Vermont. A, Ventral valve sliow- 

 ing pedicle furrow (j))- B, Cardinal 

 View showing tlie open and unmodified 

 pedicle opening. i/i (after Walcott). 



>^-^, 



U 



9 



Fig. ,543. 



Paterina superha Walcott. Middle Cambrian ; Vermont. 

 A-C, Views of the ventral valve showing the large convex 

 homoeodeltidium. D, Exterior of dorsal valve. '■^/.^ (after 

 Walcott). 



Subgenera : Micromitra Meek; and Iphidella Walcott (Iphidea Billings 1872, non 

 Baly 1865). Shell in the former more or less ornamented by crenulated 

 concentric lines, while the latter has diagonally intersecting rows of pits. 

 Lower and Middle Cambrian ; North America. 



Volhorthia von Möller. A globose form of Paterina, with well-developed 

 pseudodeltidia. Ordovician ; Esthonia. 



Mickwitzia Schmidt. Very large round forms with more or less ornate 

 exteriors. Lower Cambrian ; Esthonia, Sweden, America. Causea Wiman 

 is regarded by Walcott as probably identical with Mickwitzia, Lower 

 Cambrian ; Sw^eden. 



Superfamily 2. KÜTORGINACEA Walcott and Schuchert. 



Progressive, thick-sheUed, almost calcareous atrematous-like shells, tending to he 

 transverse and developing rudimentary articulation, more or less rudimentary cardinal 

 areas, homoeodeltidia and muscle scars prophetic of the Protremata. Derived out of 

 Rustellacea. Cambrian. 



Family 1. Schuchertinidae Walcott. 



Primitive round Kutorginacea with small cardinal areas. Externally like Obolus, 

 with an open subtriangular delthyrium which apparently is without a homoeodeltidium. 

 Muscle scars and vascular markings prophetic of the Billingsellidae of the Protremata, 

 Cambrian. 



Schuchertina Walcott (Fig. 544). Middle Cambrian ; Montana. 



Family 2. Kutorginidae Schuchert. 

 Progressive transverse Kutorginacea with rudimentary cardinal areas, great 



