396 MOLLUSCOIDEA phylüm v 



■ Camarophorella Hall and Clarke; Biconvex, sub-circular Camarophoriae, 

 biit without sinus, f old and plications. Lower Carboniferous ; North America. 



Strophomenacea of unknown relationships. 



Family 1. Eichwaldiidae Schucliert. 



Primitive or aberrant, rostrate Strophomenacea, with narrow lateral grooves and 

 ridges for articulation. Delthyrium closed hy a concave plate {? deltidium). Pedicle 

 emerging through the ventral umhone and moving with growth anteriorly hy resorption 

 through the shell, as in Siphonotretidae. Ordovician and Silurian. 



Eichwaldia Billings. The single species of this genus has a smooth 

 exterior. Ordovician ; North America. 



Dictyonella Hall {Eichwaldia auct.). Exterior surface of valves pitted in 

 quincunx, resembling Trematis. Silurian ; North America, England, Bohemia 

 and Gotland. 



Order 4. TBLOTRBMATA Beecher. 



Specialised (through Atremata, ? Obolacea), articulate, calcareous Brachio- 

 poda, with the pedicle opening shared hy both valves in earliest shell ed 

 stages, usually confined to one valve in later stages, and becoming more or less 

 modified by deltidial plates in advanced growth stages. Brachia supported by 

 calcareous crura, loops or spiralia. 



Superfamily 1. RHYNCHONELLACEA Schuchert. 



Rostrate, primitive Telotremata, with or without crura for the support of the 

 hrachidia. Pedicle foram^n nearly always heneath the heak and hut rarely through 

 a truncate ventral apex. Shells almost always impunctate. Ordovician to Recent. 



Family 1. Protorhynchidae Schuchert. 



Primitive Rhynchonellacea without deltidial plates or crura. Ordovician. 



Protorhyncha Hall and Clarke. Biconvex Rhynchonellae with the fold 

 and sinus ill-defined. No cardinal process or dorsal median septum. Surface 

 with low radial plications. Ordovician ; North America. 



Family 2. Rhynchonellidae Gray. 



Rhynchonellacea with crura of greater or lesser length. Shells usually plicate, 

 rarely smooth or spinöse. Ordovician to Recent. 



Subfamily A. Rhynchotreminae, novum. 



Rhynchonellids with a cardinal process. Ordovician to Devonian. 



Orthorhynchula Hall and Clarke. Rhynchonellae with short, straight hinge- 

 line and cardinal areas in both valves, bisected mesially by open delthyria. 

 Teeth unsupported by dental lamellae. A linear cardinal process present. 

 Ordovician ; North America. 



Rhynchotrema Hall (Stenochisma Conraid, 1839; and Hall, 1867) (Fig. 590). 



