SÜBCLASS II 



EUCRUSTACEA— OSTRACODA 



739 



Family 3. Cytheridae Zenker. 



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

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

 denticulated, the right valve with 

 two teeth in most cases, and the left 

 with corresponding pits. 



Fossil species of this family are 

 very numerous in the marine deposits 

 of the Cretaceous and Tertiary. The 

 resemblance between Cythere and the 

 Devonian genus Strepula is so decided 

 as to indicate relationship. 



Cythere Müller (Fig. 1426, a). 

 Shell reniform or subquadrate, 

 usually widest in front ; surface 

 variously ornamented ; hinge teeth 

 strong, placed one at each end of 

 a horizontal bar which fits into a corresponding furrow and sockets of the left valve. 

 Permian to Recent. 



Gythereis Jones (Fig. 1427). Like Cyther 

 wanting. Cretaceous to Recent. 



Gytheridea Bosq. (Fig. 1426, c). Differs from Cythere in having hinge beset with 



Fig. 1426. 



Valves of fossil Ostracoda. a, Cythere hassleri Ulr. x l^/j. 



h, Cytheropterorv nochsum Ulr. and Bass. x 17/]. c, Cytheridea 



2)erarcuata Ulr. x ^%. d, Pachydomella tumida Ulr. x l4/j. 



e, Xestoleberismuelleriana(ha.m.). X 30/j. f, Octonaria Stigmata 



X 18/i. 



but connecting bar of the hinge is 



Ulr. 



Fio. 1427. 

 Gythereis quadrilatera Roeraer. Gault ; Folkestone, England, x 25/j (after T. Rupert Jones). 



row of small teeth in right valve, often interrupted in the middle, and with corre- 

 sponding pits in the left valve. Jurassic to Recent. 



Cytherideis Jones. Shell more or less triangulär ; hinge simple. Cretaceous to 

 Recent. 



Carbonia Jones. Carboniferous. Cytheropteron (Fig. 1426, h), Xestoleberis (Fig. 

 1426, e) and Pseudocythere Sars. Tertiary to Recent. 



Family 4. Thlipsuridae Jones. 



Reniform or ovate inequivalve shells^ less than 2 mm. in length, the margin of one 

 valve overlapping that of the other more or less completely ; dorsal margin arcuate, 

 ventral sometimes straight or slightly sinuate. Surface with two or more deßnite pits. 



Thlipsura Jones and Holl. Valve generally with three pits, one posterior and two 

 in the anterior half. No ornament. Silurian and Devonian. 



Octonaria Jones (Fig. 1426, /). Differs from the last in having the surface of 

 valves raised into a thin spiral or annular ridge which in the more typical forms is 

 8-shaped. Silurian and Devonian. 



Phreatura J. and K. Posterior end of shell strongly compressed and marked by 

 a shallow semicircular pit ; a similar but smaller pit is present at the anterior 

 extremity. Carboniferous. 



