644 ARTHROPODA 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. 
Family 2. Beyrichiidae. Jones. 
Small equivalve Ostracoda with a long straight hinge. Shells vertically suleated 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 suleus, 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 suleus. Ordovician. 
Aechmina, Jones and Holl. Like Primitia, but having 
instead of the sulcus a single, sometimes enormously developed 
Fic. 1339. horn-like process. Ordovician to Devonian. 
Primitia _prunella, Barr. Eurychilina, Ulrich. Oblong or semi - elliptical shells 
Silurian (5 jhonisshot, having a sub-central Primitian suleus, the posterior edge of 
Bohemia (after Barrande). 5 ’ P 8 
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 Fic. 1340. Fig. 1341. 
the other two. The outer ones are some- _Peyrichiatuberculata, Beyrichia Bohemica, 
. = x Kléden. Silurian erratic ; Barr. Ordovician; 
times connected ventrally, and are not Brandenburg. Vinice, Bohemia. 
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. 
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. 
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