CRUSTACEA— OSTRACODA. 337 



^g. Ridge curved parallel to basal margin or partly so 4f. 



4-f. With continuous or discontinuous nodes, ridge complete. 



XX. Drepanella, 

 4|. With spines instead of nodes, ridge continuous. 



XIX. Dicranella, 

 4f. Without nodes or prominent spines, ridge continuous or dis- 

 continuous **. 



^*. Surface smooth (except for small anterior spines in one 

 species), marginal ridge often discontinuous..XXT. Moorea. 



^*. Surface with twisted ridges z''. 



2.^' . Ridges few and S-shaped, one partly enclosed by in- 

 complete marginal rim XXII. Strepula. 



2'^ . Ridges numerous, dividing and mostly longitudinal. 



XXXVII. Kirkbya. 

 2/\ Ridges ring-like, or forming figure 8. 



XXIII. Octona via . 

 88. Ridge broad, nodes strong XXXI. Scojieldia. 



f. Surface without curved ridges, but with strong dorsal spine. 



XII. ALch ni ina . 



4. With more or less well developed marginal flange or frill .g. 



g. Flange extending around most of the valve, radiately striated, surface 

 pitted, base swollen, a rounded posterior and elongate anterior node 

 present XXXII. Treposella. 



g. Flange extending only part way around ventral margin, not distinctly 

 striated — a large median round and a smaller posterior round node 



present, besides minor nodes or spines XXXIII. Hollina. 



B. Dorsal edge more or less curved or irregular; hinge-line within or below it II. 



II. Valves without teeth, surface mostly smooth 5. 



5. Surface without median depression k. 



h. Shell extremely ventricose 99. 



99. Left valve the larger, overlapping the right ; no depressed spot or 



pit XXXIX. Pachydomella. 



99. Right valve the larger, overlapping the left, with subanterior de- 

 pressed spot or pit XXXVIII. Barychilina. 



h. Shell of moderate convexity 000. 



coo. Valves overlapping dorsally as well as ventrally hh. 



hh. Left valve the larger 5f. 



5f , Form elongate *^*. 



**^. Right valve with posterior spinose prolongation. 



XL. Krausella. 



***. Without spinose prolongation XLV, Byihocypris. 



5f. Form subtriangular or rhomboidal XLIII. Bairdia. 



hh. Right valve the larger XLVIII. Cytherella. 



000. Valves overlapping ventrally but not dorsally ii. 



ii. Greatly elongate, thickest in center, pointed posteriorly. 



XLIV. Pontocypris. 

 ii. Moderately elongate, wedge-shaped, thickest posteriorly, hinge 



toothed XLIX. Metacypris. 



ii. Reniform or oval 6f . 



6f . With anterior or ventral hook-like projection. 



XLVI. Cy pride a. 



