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. 



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

 supported or free spondytia, and, as a rule, cruralia. Deltidia and chilidia 

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

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



. Family 1. Syntrophiidae Schuchert. 



Primitive transverse Pentaiaerids, 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). Rostrate, plicate, small and rare shells, 

 with a free but small spondylium. Lower Cam- 

 brian : North America. 



ml 



Fig. Ö83. 



Stvantonia antiquata (Bill.). 

 Lower Cambrian ; Vermont. A, 

 Ventral exterior. B, Side view 

 of same showing spondylium 

 (after Walcott). 



Fig. 584. 



SyntropMa lateralis (Whitfield). Ordovician ; Fort Cassin, 

 Vermont. A, C, D, E, Views of ventral valve showing cardinal 

 area and spondylium. B, Dorsal valve. F, Cardinal view of 

 both valves ground away to sliow 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 spondylium is supported by 

 three septa. Lower Ordovician ; Montana. 



Family 2. Olitambonitidae Winchell and Schuchert. 



Divergent transverse Pentamerids, derived out of Syntrophiidae, with well- 

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

 ally Ordovician but ränge sparingly into Devonian. 



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

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



