200 Professor T. Rupert Jones — 



This form as figured in the " Isis," 1879, is obliquely ovate 

 (PI. VIII, Fig. 10) in general outline. In the " Verstein. Sachsen," 

 1855, it is shorter and subcircular in outline (Fig. 9). Possibly 

 a sexual difference. 



In figs. 2a, 2a (1879) the umbonal convexity is subovate in out- 

 line ; and the flat marginal area is much narrower in front than 

 behind (Fig. 10). The flat margin is narrow and less distinct than 

 in figs, la, 7a (1855). In the latter (Fig. 9) the umbonal convexity 

 is more nearly subcircular in outline, and the flat marginal area 

 broader and more distinct than in figs. 2a, 2a (Fig. 10). The strong 

 concentric ridges on the convex portion and the very delicate lines 

 on the flat parts are well shown, especially in fig. 7a. 



§ V. 3, EsTHERiiNA LiMBATA (Goldenberg), 1877. 

 PLATE VIII, Fig. 11. 



Estheria Umbata, Goldenberg, Fauna Sargepontana Fossilis. Heft 2, 

 1877, p. 43, pL ii, figs. 12 and 14. 



The figures of this " Estheria limhata," from the Coal-shale near 

 Wemmetzweiler in the Saarbriicken Coalfield, indicate a similar 

 unusual convexity at the umbo of the valve. This form appears to 

 have about 24 concentric riblets, with square- celled interspaces. 

 Of these lines of growth, 15 are strong and prominent on the 

 umbonal region, which is more convex than the rest of the surface ; 

 the other concentric riblets are smaller and closer together, "mere 

 lines," on the narrow and flat marginal area or border, whence 

 originated the name " Umbata.'" 



Fig. 12, magnified six diameters, appears to represent a specimen 

 measuring as follows — 



Size. — Valve, length 4-0 mm., height 3*0 mm. ; umbonal convexity, 

 length 3'Omm., height 2-5 mm. 



Fig. 14, magnified fourteen diameters, represents a specimen — 



Size. — Valve, length 3-6 mm., height 2-4 mm. ; umbonal convexity, 

 length 2"4 mm., height 20 mm. 



It is evident the Brazilian specimens described above, with 

 the umbonal swelling or prodissoconchal boss, differ from both 

 E. Freysteini, Geinitz, and E. Umbata, Goldenberg, by the dorsal 

 convexity having a much smaller area in relation to the size of the 

 valves, and by the other part of the valve in the Brazilian form 

 being expanded to a much greater extent. In its general outline 

 the latter differs from the foregoing European species, although 

 approaching in shape to E. Freysteini as figured in the " Isis," 

 1855 (PI. VIII, Fig. 9). 



If we take advantage of G. 0. Sars' careful researches in the 

 life-history of some Estherian forms,' we may see that such a 

 persistent swelling near the umbo, as we have in the hump-backed 

 fossils here mentioned, may be said to represent the partly developed 

 test, in its early stages of existence, not so much in the larval 



' Christiania Vidensk.-Selsk. Forhandl. '1887, No. I; Oyclestheria Hislopi, 

 p. 8 et seq., pis. i and ii, vii and viii. Arcliiv. Math, og Naturw., vol. viii, 

 pt. 1, June, 1896 ; Istheria Fac/cardi, pp. 1-27, pis. i-iv. 



