320 



MOLLUSCOIDEA BRACHIOPODA 



SUB-KINGDOM V 



Superfamily 2. PENTAMERACEA. Schuchert. 



Derived Protremata with spondylia, to which are attached the adductor, diductor, 

 and ventral pedicle muscles. Cruralia commonly pi'esent. Ordovician to Permian. 



Family 1. Clitambonitidae. Winchell and Schuchert. 



Primitive Pentameracea with long, straight cardinal areas and a well-developed 

 deltidium. No cruralium. Ordovician to Devonian. 



Clitambonites, Pander (Orthisina, d'Orb., Pronites, Hemipi-onites, and Gomi.m- 

 bonites, Pander), (Fig. 538). Valves convex or sub -pyramidal. Hinge-line 

 straight, forming the greatest diameter of the shell. Cardinal area of the 



ventral valve high ; 

 delthyrium broad, 

 and covered by a 

 perforate deltidium ; 

 that of the dorsal 

 valve covered by a 

 chilidium. Dental 

 lamellae of ventral 

 valve very strongly 

 FlG ' 53S ' developed, uniting 



A, Orthisina adscemtens, Pand. Ordovician ; Pawlowsk, near St. Petersburg. J 



i/i. B, C, 0. squamata, Pahlen. Ordovician ; Kuckers, Esthonia. B, Interior of tO lOrm a COllCave 



dorsal valve, showing edge of the chilidium. C, Interior of ventral valve, showing ar ,of nlofa -nlafp or 

 spondylium, septum, and deltidium (after Pahlen). 



spondylium. This 



plate serves for the attachment of muscles, and is supported by a median 

 septum extending for about one-half the length of the valve. External 

 surface radially striated. Shell substance impunctate. Ordovician ; Russia, 

 England, and North America. 



Polyfoechia, Hall and Clarke. Like Orthisina, but with the spondylia sup- 

 ported by three septa, thus dividing the umbonal cavity of the ventral valve 

 into five chambers. Ordovician ; North America. 



Scenidium, Hall (Mystrophora, Kayser). Small Orthisinoid shells with the 

 delthyrium partially closed by a concave imperforate deltidium. Cardinal 

 process extending as a median septum throughout the length of the shell. 

 The septum is sometimes greatly elevated anteriorly in Devonian species. 

 Ordovician to Devonian ; North America, Europe, and the Urals. 



Family 2. Syntrophiidae. Schuchert. 



Primitive Pentameracea with long, straight cardinal areas, deltidia, and cruralia. 

 Lowest Ordovician. 



Syntrophia, Hall and Clarke. Transverse, straight - hinged, primitive 

 Pentameroids. North America. 



Family 3. Porambonitidae. Davidson. 



Pentameracea intermediate in structure between the Syntrophiidae and Penta- 

 meridae ; the deltidium ana the straight cardinal areas of the former family tending 

 to obsolescence, particularly the deltidium. The Porambonitidae approach the latter 



