198 Professor T. Rupert Jones — 



'■• § III. 1, EsTHERiiNA Bresiliensis, gen. et sp. nov. 



PLATE VIII, Figs, la-c, la, h, 3, 4, 5. 



Valves subovate, with the earliest (uinbonal) part of the valve 

 very much more convex than the other part of the surface, and 

 looking like an exaggerated growth of what had been prodisso- 

 conchal.^ This neanic portion diffei's somewhat in colour, and 

 probably ia intimate structure to some extent. The outline of 

 different specimens varies according to their stages of growth 

 and sexual form ; also by their having been subjected to pressure 

 during fossilization. On the limited umbonal convexity, the lines of 

 growth are marlied by eight or nine concentric ridges, relatively 

 coarse, and wide apart ; whilst on the lower and outer, expanded, 

 flatter, newer part of the valve the ridges of the lines of growth are 

 thinner, much closer together (thirty or more), and neatly beaded 

 with projections, probably the modified bases of earlier setae. Near 

 the edge of the valve this ornament becomes a mere crenulation on 

 the close-set concentric ridgelets (Fig. Ic). 



The interstitial ornament consists of a delicate and crowded 

 pitting (Figs. 16, Ic). 



The valves are black, thin, and apparently chitinous, sometimes 

 glossy on the boss or umbonal swelling; which, therefore, seems to 

 be somewhat different in constitution ; moreover, in some individuals 

 it is of a brownish tint. 



Fig. 1, a right-hand valve, much flattened and otherwise modified, 

 is relatively the shortest and highest of the best specimens. It has 

 a broad and blunt oval outline. In dark-coloured greenish-black 

 fissile shale, with ferruginous staining on some bed-planes ; some 

 lara nse are sub-bituminous ; some faces glazed and slickensided. 

 With fish-remains. 



Size. — Valve, length 6'4 mm., height 5 mm. ; umbonal convexity, 

 length 3'6 mm., height 2-4 mm. From a cutting on the Bahia and 

 San Francisco Railroad at kilometre 5 from Bahia, near the viaduct. 



Fig. 2, slightly crushed, has a subovate outline, much narrower 

 posteriorly than Fig. 1. From the same dark shale, with fish- 

 remains, at kilometre 4 on the railroad. 



Size. — Valve, length 5 6 mm., height 3-2 mm. ; umbonal convexity, 

 length 1"6 mm., height 1 mm. 



Besides this perfect valve there are on the same slab several, 

 imperfect valves and a pair in position, but not perfect ; also three 

 separate umbonal bosses, one of them shiny. 



Figs. 1 and 2, differing by either variety, sex, or stage of growth, 

 appear to represent the normal form. 



Figs. 3 and 4 represent the edge view and the end view of the 

 carapace, somewhat diagrammatically. 



Fig. 5, from the same dark shale, a little nearer to Bahia (at 3"85 

 kilom. on the railroad), " near the junction of the Cretaceous with 

 the Gneiss," shows two valves in apposition, umbo to umbo, opened 



1 The prodissoconch is more or less persistent in some bivalved Molluscs, as 

 Sphcerium, Pisidium, Ostrea, Avicula, etc. 



