ORDER III 



PROTREMATA 



321 



in tending to develop a rostmfr ^<-iL <'r>i<-lutm present. Ordovician to 

 Lower Devonian. 



Camarella (Billings), Hall and Clarke. Small smooth shells with a few low 

 ])lications and without cardinal areas. Dorsal valve at maturity most convex. 

 Spondylium well defined. Cruralium very small, supj)orted by a long septum. 

 Ordovician ; North America and (?) England. 



/V/VS//VY//,,,,, Hall and Clarke. Much like Camarella, but with a moderately 

 long, straight, cardinal line, and no cardinal area. Dorsal umbo conspicuous, 

 projecting beyond that of the ventral valve. Ordovician and Silurian; North 

 America and England. 



Anastrophia, Hall (Brachymerus, Shaler, non Dej.) Much like Parastrophia, 

 but with the dorsal umbo more prominent and the valves with numerous sharp 



FIG. 539. 



Porambonites wqnirostris, Schloth. sp. Ordovician (Vaginateukalk) ; St. Petersburg. A~C, Anterior, lateral, 

 iiinl IM Verier aspects of shell, Vi- A Punctate surface, magnified. E, F, Interior of ventral and dorsal valves, 

 respectively. 



plications extending to the beaks. Silurian and Lower Devonian ; North 

 America, England, and Gottland. 



Porambonites, Pander (Is&rhynchuSj King), (Fig. 539). Shells similar to 

 Parastrophia in form, but without plications, and with obtusely triangular 

 areas in both valves. Shells thick, variously pitted externally. Ordovician ; 

 Russia. 



Noetlingia, Hall and Clarke. Exterior like Porambonites, but with long, 

 straight, hinge-line, prominent cardinal areas, and perforate beaks. Ordovician ; 

 Russia. 



? Lycophoria, Lahusen. Russia and Scandinavia. 



Family 4. Pentameridae. M'Coy. 



Rostrate Pentameracea rarely with straight cardinal areas. Deltidium commonly 

 absent, but sometimes present as a concave plate, being the reverse of the ordinary form 

 of the deltidium and due to the incurved beaks. Cruralium present. Silurian to 

 Permian. 



Conchidium, Linn (Gypidia, Dalman ; Antirhynchonella, Quenstedt ; Zd'nnir, 

 Barrande), (Fig. 540). Shell strongly iiiequivalve, biconvex, with highly 

 arched ventral valve. Surface numerously plicated. Spondylium narrow and 

 deep, and supported by a high vertical septum of variable length. A small 

 cardinal process present. Silurian and Devonian ; distribution general. 



Stricklandinia, Billings. Similar to Conchidium, but with a straight hinge- 

 line and no prominent arched ventral beak. Spondylium small and short, 

 supported by a short median septum. Silurian ; North America, England, 

 and Gottland. 



Pentamerus, Sowerby (Pentastere, Blainville). Like Conchidium, but with 

 VOL. i Y 



