papa aut | PROTREMATA 32] 
family in tending to develop a rostrate shell. Cruralium present. Ordovician to 
Lower Devonian. 
Camarella (Billings), Hall and Clarke. Small smooth shells with a few low 
plications and without cardinal areas. Dorsal valve at maturity most convex. 
Spondylium well defined. Cruralium very small, supported by a long septum. 
Ordovician ; North America and (7) England. 
Parastrophia, 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 

Porambonites aequirostris, Schloth. sp. Ordovician (Vaginatenkalk) ; St. Petersburg. A-C, Anterior, lateral, 
and posterior aspects of shell, 1/;. D, Punctate surface, magnified. 2, F, Interior of ventral and dorsal valves, 
respectively. 
plications extending to the beaks. Silurian and Lower Devonian; North 
America, England, and Gottland. 
Porambonites, Pander (Isorhynchus, 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, Linné (Gypidia, Dalman ; Antirhynchonella, Quenstedt ; Zdimir, 
Barrande), (Fig. 540). Shell strongly inequivalve, 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 Conchidiwm, 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 (Pentastire, Blainville). Like Conchidiwn, but with 
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