736 ARTHKOPODA phylum vii 



one of mandibles, two of maxillae, and two pairs of feet. Abdomen short and 

 riLdimentary. 



As a ruie only the bivalved shell of the.Ostracoda is found fossil, and since 

 the Classification is based principally upon characters presented by the 

 appendages, the relations of recent to fossil forms cannot be made out with 

 certainty, especially as the form and ornamentation of the shell are largely 

 independent of the internal Organisation. 



The valves are closed by a subcentral adductor muscle, the attachment of 

 which is marked on their inner sides by a tubercle, pit, or a number of small 

 spots. The shell is compact in structure, commonly from 0*5 mm. to 4 mm. 

 in length, although sometimes exceeding 20 mm. The outer surface may be 

 smooth and glossy, or granulöse, pitted, reticulose, 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 or 

 left valve overlapping at the ventral border only (Leperditia), or at the dorsal 

 border as well (Bairdia), or in some cases overlapping all round (Cytherella). 



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 

 anterior, even though of equal or of less height. The hinge -line may be 

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

 the Cytheridae hinge teeth and corresponding sockets are often developed. 

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



Mem. Soc. Roy. Sei. Liege, 1847, vol. iv. — Description des Entomostraces fossiles des terrains 

 tertiaires de la France et de la Belgique. Mem. Couronn. Acad. Roy. Belg., 1850, vol. xxiv. — 

 Monographie des crustaces fossiles du terrain cretace du Duche de Limburg. Mem. Commiss. Carte 

 geol. Nederlande. Haarlem, 185i. —Reuss, A. E., Die fossilen Entomostracen des österreichischen 

 Tertiärbeckens. Haid. naturw. Abhandl., 1850, vol. iii., pt. 1.— Die Foramiiiiferen und Entomo- 

 stracen des Kreidemergels von Lemberg. JMd. iv., pt. 1, lS61.~Jones, T. R., A Monograph of 

 the Entomostraca of the Cretaceous Formation of England. Palaeont. Soc, 1849.— Idem, and 

 Hinde, G. J., A Supplemental Monograph of the Cretaceous Entomostraca of England and Ireland. 

 Ibid., 1890.— Jones, T. R., A Monograph of the Tertiary Entomostraca of England. Ibid., 1857. 

 —Idem, and Sherborne, C. I)., A Supplemental Monograph of the Tertiary Entomostraca of 

 England Ibid., 1889.— Jones, T. R., and Kirkby, J. W., Notes on Palaeozoic bivalved Entomostraca, 

 Nos. 1-32. Ann. Mag. Nat. Hist., 1855-95.— Ä'^rprer, ()., Die Ostracoden der Miocänschichten bei 

 Ortenburg Neues Jahrb., 1858. -^Sjpeyer, 0. W. C, Die fossilen Ostracoden aus den Casseler 

 Tertiarbddimgen. Cassel Jahresber., 1863, vol. xiil-Brady, G. S., Crosskey, H. W., and 

 Robertson, D.,k Monogi-aph of the Post-Tertiary Entomostraca of Scotland. Palaeont. Soc, 1874. 

 -Jones, T. R Kirkby, J. W^nd Brady, G. S., A Monograph of the British Fossil bivalved 

 Entomostraca from the Carboniferous Formations. Ibid., 1874, \884..-Jones, T. A., and Holl, 

 H. B Notes on Palaeozoic bivalved Entomostraca. Ann. Mag. Nat. Hist., 1869, ser. 4, vol. iii.- 

 ^Zf^' Ä^; ;'• *"^^^'!i«f' ■^- ^-^ A Monograph of the marine and fresh-water Ostracoda of the 

 Monn^tnW i'' o / ,''' T^"""' i^^^" ^"^^^"^ ^"^^ ^889-96, vols. iv., V . - Lienenklaus, K, 

 Monographie der Ostracoden des nord westdeutschen Tertiärs. Zeitschr. Deutsch. Geol. Ges., 1894, 



Trans R;TSin\f'i«S« ^T^^^' ^^^ ,'^" ^" Carboniferous Ostracoda from Ireland: Sei. 

 Geol M^nn" pLl plf ' 1 "' ""'l' 'o To^^''^' ^' ^^ ^^e Lower Silurian Ostracoda of Minnesota. 

 Sat Sd 1897 vo? v' ^1-- "'•^?*- ^' IP^—^herborn, C. D., The literature of fossil Ostracods. 

 Zeitschr Dent^;rV^;rr''''^^^^^^^ ^^.^'^ Tertiär-Ostrakoden des mittleren Norddeutschlands. 

 Ber tnckenber^Nt rp?'F l^?' 'A^r^'^''''^ ^'^ Ostrakoden des Mainzer Tertiärbeckens. 

 R^ckfirCaDe Brefon ■ r 'nfr^ ^'^' .l^OÖ-J/a^^Äe.., G. F., Ostracoda of the basal Cambrian 

 ^f Phvlloeari<fa Proo P^^^^ T' ^>^^.^^^ "°^- ^^^-Ohapman, F., Son.e Silurian Ostracoda 

 Ä / ^TneHean Palen^^^^ fw" ^^f"""' ^^^4' "• «' ^^^' ^^n.-Ulrich, E. 0., and Bassler, 

 Ä. *3., jNew American Paleozoic Ostracoda, pts. ii. and iii Proo TT q NnV M,i« lonfiiQOS 

 vol,. XXX., xxxv.-Miocene Ostracoda. Maryland Geol. Surv, Siocte Vot 1904 - ' ' 



