738 



ARTHROPODA 



PHYLUM VII 



Primitia Jones and Holl (Fig. 1425, b). Has well-marked subcentral pit or 

 sulcus, with furrow extending to the hinge line. Ordovician to Permian. 



Dicranella Ulr. (Fig. 1425, d). Like Primitia but has horn-like process on one 

 or both sides of the sulcus. Ordovician. 



Aechmina J. and H. (Fig. 1425, c). Sulcus is replaced by a single, horn-like 

 process. Ordovician to ]\Iississij)pian. 



Ulrichia Jones. Ordovician to Mississippian. Synafhe, Beyrichiopsis, Beijrichiella 

 Jones and Kirkby. Carboniferous. 



Eurycliilina Ulr. (Fig. 1425, g). Like Primitia but ventral margin provided 

 with a wide, frill-like border. Ordovician and Silurian. 



JoneseUa Ulr. (Fig. 1425, /). Valves subovate with a ci;rved ridge on the 

 posterior two-thirds. Ordovician and Silurian. 



Fig. 14-25. 



Paleozoic Ostr<Koda. a, Primitiellu unicornis Uli-. x i^/i- ''> Pi'imitia fincinnatieiisis Miller, x i-*/i. c, 

 AechmiTM marginata Ulr. X I'l/j. d, Dicranella bicornis Ulr. x ii^/i. e, Ctenobolhina ciliata Emmons, x s/j. 

 /, Jonesella crepidifurmis Ulr. x '^-/i. g, Eurychilina reticulata Vlr. x 'O/i. /(, Halliella IdbrosaXSlr. x i'*/!. 

 i, Kloedenia centricornis Ulr. and Bass, x I'l/j. j, Tetradella qiiadrilirata H. and W. x i3/j. fc^ Ceratopsis 

 chambersi Miller, x i2/j. l^ Kloedenella iurgida Ulr. and Bass, x I'l/i. in, Kirkbya tnibqxifulrata Ulr. x ^-i/i. 

 n, Beynchia clavata Kal. x i-i/i. o, Drcpanella crasHnoda Ulr. x i"/]. p, Dilobcfla typa Ulr. x i^/i. 



Bollia Jones and Holl. Valves with a central looped or horseshoe-shaped ridge. 

 Ordovician to Mississippian. 



Tetradella Ulr. (Fig. 1425, j). Valves marked l)y four more or less curved 

 vertical ridges united ventrally. Ordovician and Silurian. 



Geratofsis Ulr. (Fig. 1425, k). Has a horn-like process arising from the ex- 

 tremity of the jjosterior ridge. Ordovician and Silurian. 



Gtenoholbina (Fig. 1425, e), Drepanella (Fig. 1425, o), Halliella Ulr. (Fig. 1425, 

 h). Ordovician to Devonian. 



Beyrichia M'Coy (Fig. 1425, n). Valve has three lobes or nodes with the central 

 one the smallest. Ordovician to Devonian. 



Kloedenia Jones and Holl (Fig. 1425, i) ; Kloedenella Ulr. and Bass. (Fig. 

 1425, Z). Silurian and Devonian. Dilobella Vlr. {Fig. IA25, p). Ordovician. Hollina, 

 Jonesina, Treposella Ulr. and Bass. Devonian to Carboniferous. 



The following genera, doubtfully referred here, should perhaiJs be regarded as 

 Paleozoic Cytheridae : 



Kirkhya Jones (Fig. 1425, m). Devonian to Permian. Moorea J. and K. 

 Ordovician to Permian. Strepula J. and H. Silurian and Devonian. Macronotella 

 Ulr. Ordovician, 



