^38 ARTHROPODA phylüm vii 



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

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



mcZella Ulr. (Fig. 1425, d). Like Prirrntia but has horn-hke process on one 

 or both sides of the sulcus. Ordovician. , -, , • ^ x. vi 



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

 process. Ordovician to Mississippian. 



Ulrichia Jones. Ordovician to Mississippian. Synaphe, BeyncUops%s, Beynchiella 

 Jones and Kirkby. Carboniferous. . . . , . -, • -a a 



Eurychilina Ulr. (Fig. 1425, g). Like Pn'mi^a but ventral margm provided 

 with a Wide, friU-like border. Ordovician and Silunan. 



/ones^i^« Ulr. (Fig. 1425, f). Valves subovate with a curved ridge on the 

 posterior two-thirds. Ordovician and Silurian. 



Fig. 1425. 



Paleozoic Ostracoda. a, Primitiella unicornis Ulr. x i4/i. b, Friniitia ci-ricinnatiensis Miller, x i^/i. c, 

 .4ecfcmiTio margitiata Ulr. x i4/j. d, Dicranella hicornis Ulr. x lo/i. e, Ctenobolbina ciliata Emmons, x ^/i- 

 f, Jomsdla crepidiformis Ulr. x ^2/^. g^ Eurychilina reticulata Ulr. x lO/j. h, Halliella labrosa Ulr. x ^4/^, 

 i, Kloedenia centricornis Ulr. and Bass. x i^/^. j, Tetradella quadrilirata H. and W. x i3/j. fc, Ceratopsis 

 ckambersi Miller, x i2/j. i^ Kloedenella turgüki Ulr. and Bass. 

 n, Beyrichia clavata Kai. x i^/j. o, Drepanella crasdnoda Ulr. 



l4/i, m, Kirkhya subquadrata Ulr. X ^^/j. 

 X lO/j. Pj Dilohella typa Ulr. x l^/j. 



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

 Ordovician to Mississippian. 



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

 vertical ridges united ventrally. Ordovician and Silurian. 



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

 tremity of the posterior 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, i). Silurian and Devonian. Dilohella Vir. (Fig. 14:25, p). Ordovician. Hollina, 

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



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

 Paleozoic Cytheridae : 



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

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

 Ulr. Ordovician. 



