736 ARTHEOPODA phylum vii 



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

 rudimentary. 



As a rule 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 granulose, 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. Sci. Lk'ge, 1847, vol. iv. — -Description de.s Entomostraces fossiles des terrains 

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

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

 geol. Nederlande. Haarlem, 1854. — Reuss, A. E.. Die fossilen Entomostracen des osterreichisclien 

 Tertiiirbeckens. Haid. naturw. Abhandl., 1850, vol. iii., pt. 1. — Die Foraminifereu mid Entomo- 

 stracen des Kreidemergels von Lemberg. Ibid, iv., pt. 1, 1851. — Jones, T. M., 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, G. I)., A Supplemental Monograph of the Tertiary Entomostraca of 

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

 Nos. 1-32. Ann. Mag. Nat. Hist, 1855-95. — Egger, 0., Die Ostracoden der Miociinschichten bei 

 Ortenburg. Neues Jahrb., 1858. — Speyer, 0. W. C, Die fossilen Ostracoden aus den Casseler 

 Tertiiirbildungen. Cassel Jahresber., 1863, vol. xiii. — Brady, G. S., Orosskey, H. W., and 

 Robertson, D., A Monograph of the Post-Tertiary Entomostraca of Scotland. Palaeont. Soc, 1874. 

 — Jones, T. R., Kirkby, J. W., and Brady, G. S., A Monograph of the British Fossil bivalved 

 Entomostraca from the Carboniferous Formations. Ibid., 1874, 1884. — Jones, T. A., and HoU, 

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

 Brady, G. S., and Norman, A. M., A Monograjih of the marine and fresh-water Ostracoda of the 

 North Atlantic, etc. Sci. Trans. Roy. Dublin Soc, 1889-96, vols, iv., v. — Lienenklaus, E., 

 Monographie der Ostracoden des nordwestdeutschen Tcrtiiirs. Zeitschr. Deutsch. Geol. Ges., 1894, 

 vol. xlvi. — Jones, T. R., and Kirkby, J. W., On Carboniferous Ostracoda from Ireland. Sci. 

 Trans. Roy. Dublin Soc, 1896, vol. vi. — LIrich, E. 0., The Lower Silurian Ostracoda of Minnesota. 

 Geol. Minn., Palaeont., vol. iii., pt. 2, 1897. — Shcrburn, C. I)., The literature of fossil Ostracods. 

 Nat. Sci., 1897, vol. x. — Lienenklaus, E., Die Tertiiir-Ostrakoden des mittleren Norddeutschlands. 

 Zeitschr. Deutsch. Geol. Ges. 1900, vol. Iii. — Idem, Die Ostrakoden des Mainzer Tertiiirbeckens. 

 Ber. Senckenberg Nat. Ges. Frankfurt, 1905. — Matthew, G. F., Ostracoda of the basal Cambrian 

 Rocks in Cape Breton. Canad. Rec. Sci., 1902, vol. viii. — Chapman, F., Some Silurian Ostracoda 

 and Phyllocarida. Proc Roy. Soc. Victoria, 1904, n. s. vol. xvii. — Ulrich, E. 0., and Bassler, 

 R. S., New American Paleozoic Ostracoda, pts. ii. and iii. Proc. U. S. Nat. Mus., 1906, 1908, 

 vols. XXX., XXXV. — Miocene Ostx-acoda. Maryland Geol. Surv., Miocene Vol., 1904. 



