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 present. 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, Hemipronites, and Gonam- 
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 ; 
sss that of the dorsal 
AUS valve covered by a 
THAN S chilidium. Dental 
i Fiera lamellae of ventral 

valve very strongly 
developed, unitin 
A, Orthisine adscendens, Pand. Ordovician; Pawlowsk, near St. Petersburg. ! zi ) 
1}. B, C, O. squamata, Pahlen. Ordovician; Kuckers, Esthonia. B, Interior of tO form a concave 
dorsal valve, showing edge of the chilidium. C, Interior of ventral valve, showing : a 
spondylaun, septum, and deltidium (after Pahlen). : * spatulate plate or 
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. 
Polytoechia, 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. 
Fic. 538. 
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 and the straight cardinal areas of the former family tending 
to obsolescence, particularly the deltidium. The Porambonitidae approach the latter 
