392 



MOLLUSCOIDEA 



PHYLUM V 



modified Brachiopods are found in the Permian of China, India, Sicily and 

 Texas. 



Gemmellaroia Cossman (Megarhynchus Gem., non Lap.). Permian ; Sicily. 



Superfamily 3. PENTAMERACEA Schuchert. 



Specialised Protremata developed out of Nisusiinae among the Orthacea, with well- 

 developed, supported or free spondylia, and, as a ride, cruralia. Deltidia and chilidia 

 present in the more primitive forms and generally absent in the last developed families. 

 The least prolific stock of the Protremata. Cambrian to Permian. 



Family 1. Syntrophiidae Schucliei-t. 



Primitive transverse Pentamerids, derived out of Nisusiinae, having as a rule long, 

 straight cardinal areas that usually are devoid of deltidia and chilidia. Spondylia 

 and cruralia free or supported by septa. Cambrian and Ordovician. 



(?) Swantonia Walcott (Fig. 583). Kostrate, plicate, small and rare shells, 



with a free but small spondylium. Lower Cam- 

 brian ; North America. 



/' ' 



'a B 



Fig. .583. 



Swimtonia anthjuaUt (Bill.). 

 Lower Cambrian ; Vermont. A, 

 Ventral exterior. D, Side view 

 of same showiDi; .spondylium 

 (after Walcott). 



Fig. 584. 



Si/iitropliia laUiaUs (Whitfield). Ordovician ; Fort Cassin, 

 Vermont. A,.(', D, E, View.s of ventral valve showing cardinal 

 area and siiondylinm. ]!, Dorsal valve. F, Cardinal view of 

 both valves ground away to show section of spondylium and 

 cruralium (after Hall and Clarke). 



Syntrophia Hall and Clarke (Fig. 584). Transverse, straight-hinged, 

 primitive Pentamerids with open delthyria in both valves. Spondylia well 

 developed and supported by an incipient septum ; cruralia small and supported 

 by a septum. Middle Cambrian to Lower Ordovician ; North America. 

 Subgenus : Huenella Walcott. Has a plicate surface. Middle and Upper 

 Cambrian ; North America, China and Australia. 



Clarkella Walcott. Like Syntrophia, but the spond3dium is supported by 

 three septa. Lower Ordovician ; Montana. 



Family 2. Clitambonitidae Winchell and Schuchert. 



Divergent transverse Pentamerids, derived oid of Syntrophiidae, with well-developed 

 cardinal areas, deltidia, chilidia and spondylia. Cruralia not developed. Essenti- 

 ajly Ordovician but range sparingly into Devonian. 



Clitambonites Pander (Orthisina d'Orb. ; Pronites and Gonambonites Pander) 

 (Fig. 585). Valves convex or sub-pyramidal. Hinge-line straight, forming 



