SUPER-ORDKK 111 OSTRACODA 



smooth and glossy, or granulose, pitted, ruticiilo.se, striate, hirsute, or other- 

 wise marked, the effect being often quite ornamental. The two valves may 

 be of equal size (Beyrichia), or more or less unequal, with either the right oc 

 left valve overlapping at the ventral border only (///'y /'//'//</), or at thu dorsal 

 border as well (BairdiO,\ or in some cases overlapping all round (f /////// 



Most commonly the outline is ovate or reniform ; in many cases, however, 

 one or both ends may be pointed or drawn out in the form of a beak ; and 

 when the dorsum is straight, the ends may join it angularly. Although 

 usually convex, the ventral margin is sometimes straight or gently concave. 

 It is sometimes impossible to distinguish between anterior and posterior 

 extremities, but as a rule the posterior half is somewhat thicker than the 

 other, even though of equal or of lesser height. The hinge line may In- 

 straight or arcuate, the hinge itself being generally simple, although among 

 the Cijtherklae hinge teeth and corresponding sockets are often develoj ><!. 

 There are commonly a small median and two larger lateral eyes the position 

 of the latter being often indicated on the exterior of the valves by a small 

 " eye tubercle," or ocular spot. 



Save for one or two families (Cypridae), Ostracods are almost wholly 

 restricted to marine or brackish water. They are gregarious, and occur in 

 vast hordes swimming near the surface or creeping over the bottom, preferring 

 usually shallow depths. Their remains abound in nearly all the leading 

 formations, and are often important rock - builders. The identification of 

 fossil Ostracods is very difficult on account of their similarity of form and 

 ornamentation, and usually minute size ; and they cannot be well intercalated 

 among the recent series for reasons already given. An arrangement of the 

 families into higher groups is not attempted here, and only the more 

 representative genera can be noticed. 



Family 1. Leperditiidae. Jones. 



Thick-shelled Ostracoda, mostly of considerable size. Valves smooth and glossy, of 

 very compact structure, and in general regularly convex; hinge line straight; anterior 

 and posterior ends obliquely truncated or rounded, and neither gaping nor excised. 



Leperditia, Renault (Fig. 1337). Shell sub-oblong with an oblique backward 

 swing, from 2 mm. to 22 

 mm. long ; dorsal edge 

 straight, generally an- 

 gular at the extremities ; 

 ventral outline roun<l-d. 

 Valves unequal, the 



right larger and overlap- Flo . 13SS> 



ping ventral edge of the ''" 1337. /,.,.;,,> iioemer. 



e 



left. Surface often * ....... n ta ' ^ft. 



corneous n appearance, 



smooth, and eye tubercle generally present on the antero-doreal quarter. A large 



rounded sub-central muscular imprint present on interior. Ordovician to Carboniferous. 



Leperditelia, Ulrich. Similar to above, but the left instead of right valve is the 

 larger, and has a groove within its ventral border for receiving simple edge of the 

 right. Eye tubercle wanting. Length 1 mm. to 3 mm. Ordovician. 



Isochilina, Jones (Fig. 1338). Like Leperditia except that the valves do not over- 

 lap but are equal in every respect. Ordovician and Silurian. 



