644 



AKTHKOPODA 



SUB-KINGDOM VII 



Aparchites, Jones. Shell not over 3 mm. in length, equivalve, sub-ovate or oblong ; 

 ventral edge thickened, often bevelled. Ordovician and Silurian. 



FIG. 1339. 



Primitia prunella, Barr. 

 Silurian (E) ; Konigshof, 

 Bohemia (after Barrande). 



Family 2. Beyrichiidae. Jones. 



Small equivalve Ostracoda with a long straight hinge. Shells vertically sulcated and 

 more or less lobate, varying from forms having a simple median depression to others in 

 which the surface of the valves is raised into numerous low lobes, ridges or nodes. 



Primitia, Jones and Holl (Fig. 1339). Valves ovate or oblong, ventral margin 

 rounded, not over 2 mm. long. Well-marked sub-central pit or sulcus, with furrow 

 extending to hinge line. Cambrian to Carboniferous. 



Dicranella, Ulrich. Differs from Primitia in having long 

 horn-like diverging prominences on one or both sides of the 

 central sulcus. Ordovician. 



Aechmina, Jones and Holl. Like Primitia, but having 

 instead of the sulcus a single, sometimes enormously developed 

 horn-like process. Ordovician to Devonian. 



Eurychilina, Ulrich. Oblong or semi - elliptical shells 

 having a sub -central Primitian sulcus, the posterior edge of 

 which is often raised in to a small rounded node. Anterior, 

 ventral, and posterior margins provided with a wide, often radially marked frill-like 

 border. Ordovician. 



Kloedinia, Jones and Holl. Intermediate between Primitia and Beyrichia. Its 

 more or less well-defined small lobe between 

 the two sulci represents the median lobe 

 of Beyrichia. Ordovician to Devonian. 



Beyrichia, M'Coy (Figs. 1340, 1341). 

 Typically the valves have three lobes or 

 nodes, of which the central one is the 

 smallest, and commonly quite isolated from 

 the other two. The outer ones are some- - 

 times connected ventrally, and are not Brandenburg, 

 infrequently broken up into sets of smaller 

 nodes ; occasionally all of them are united below. Ordovician to Carboniferous. 



Tetradella, Ulrich. Valves marked by four more or less curved vertical ridges 

 which are ventrally united ; one or both of the inner ridges sometimes duplex, or all 

 four may be split up into separate nodes. Ordovician and Silurian. 



Ceratopsis, Ulrich. Distinguished from the last by the remarkable process which 

 arises from the extremity of posterior ridge. This may be straight and horn-like with 

 one of the edges toothed, or expanded. Ordovician. 



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

 the free upper extremities of which are often bulbous. Ordovician to Carboniferous. 



Drepanella, Ulrich. Valves depressed convex, sub-oblong, with a more or less com- 

 plete, often sickle-shaped, sharply elevated marginal ridge, within which the surface 

 exhibits two or more usually distinct nodes. Ordovician. 



FIG. 1340. 



FIG. 1341. 



Beyrichia Bohemica, 

 Barr. Ordovician; 

 Vinice, Bohemia. 



Family 3. Cytheridae. Zenker. 



Minute shells of generally elongate-oval, reniform, or sub-quadrate outline, and of 

 dense structure. Surface smooth, punctate, nodulose, striate or spinose ; hinge generally 

 denticulated, the right valve with two teeth in most cases, and the left with corresponding 

 pits. 



