SUBCLASS II 



EUCRUSTACEA— OSTRACODA 



739 



Family 3. Oytheridae Zenker. 



Minute shells of generally elongate-oval, reniform or sub-qioadrate outline, and of 

 dense structure. Surface smooth, imnctate, nodulose, striate or spinose ; hinge generally 

 denticulated, the right valve with 

 two teeth in most eases, and the left 

 with corresfonding pits. 



Fossil species of this family are 

 very numerous iu the marine deposits 

 of the Cretaceous and Tertiary. The 

 resemblance between Gytherc and the 

 Devonian genus Strepula is so decided 

 as to indicate relationship. 



Gythere Miiller (Fig. 1426, a). 



Shell reniform or subquadrate, Valves of fossil Ostracoda. «, Cytlwe basslcri Ulr. X H/i. 



,, -J J. ■ 4- J. r ^1 Cytheropteron nodot:u)ii Uli'. and Bass, x i''/]. c, Cytheridea 



usually widest m tront ; SUrtace perarcuata Ulr. x i-i/i. rf, Pachydomella tumida Ulr. x l^/j. 



variously ornamented • hinse teetll ^tXestulebcrismuellcriana(ham.). X •*"/!. f, OctonaHa stiginata 



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 Cy there but connecting bar of the hinge is 

 wanting. Cretaceous to Recent. 



Cytheridea Bosq. (Fig. 1426, c). Differs from Gythere in having hinge beset with 



Fli;. 1420. 



Fio. 1427. 

 Cythereis qimdrilatera Roemer. 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 triangular ; hinge simple. Cretaceous to 

 Recent. 



Carbonia Jones. Carboniferous. Gijtheropteron (Fig. 1426, 6), Xestoleheris (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. Siorface with two or more definite pits. 



Tldipsura 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. 



