370 



MOLLUSCOIDEA 



PHYLUM V 



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

 Lower Cambrian ; Vermont, 



Family 2. Paterinidae Schucliert. 



Progressive Eustellacea with the j^edide aperture more or less closed hy 

 homoeodeltidia and ■pseiidochilidia. Cambrian. 



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



Pig. 542. 



Rudella edsuni Walcott. Lower Cam- 

 brian ; Vermont. A, Ventral valve show- 

 ing pedicle furrow (/))• ^> Cardinal 

 view showing the open and immodified 

 pedicle opening, l/j (after Walcott). 



Fig. 543. 



PaterUm superha Walcott. Middle Cambrian ; Vermont. 

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

 homoeodeltidinm. D, Exterior of dorsal valve. 2/3 (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 Moller. 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 ; Sweden. 



Superfamily 2. KUTORGINACEA Walcott and Schuchert. 



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

 transverse and developing rudimentary articulaiion, more or less rudimentary cardinal 

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

 Eustellacea. Cambrian, 



F'amily 1. Schuchertinidae Walcott. 



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

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

 Muscle scars and vascular markings prophetic of the Billing sellidae of the Protremata. 

 Cambrian. 



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



Family 2. Kutorginidae Schuchert. 

 Progressive transverse Kutorginacea with rudimentary cardinal areas, great 



