156 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 17, 



wick, near Manchester, and of others found lately by Mr. Salter in 

 the Lower Carboniferous strata of Fifeshire. 



For convenience I have made the most of these differences of 

 contour, and have termed the Ardwick specimen Leaia Leidgi, var. 

 Williamsoniana ; and those from Fife, var. Salteriana ; keeping Leaia 

 Leidgi as the name for the Pottsville specimen, instead of Cypricardid 

 Leklyi. 



They are found without any immediate associates, except Plant- 

 remains and, at Ardwick, Anthracosia (JJnio) Phillipsii. 



Conclusion. — Having nothing but the carapace-valves of these 

 little Crustaceans to guide us in working out their geological history, 

 we certainly cannot pretend to know everything about them. Among 

 the living Bivalved Entomostraca, different specific forms are found 

 to have carapaces much like each other ; and, again, nearly allied 

 species have markedly different carapaces; and Estherice are not 

 without their peculiarities in this respect. Still I think we may 

 fairly believe that the marked differences of the Estherian carapaces 

 found in the several deposits really indicate distinct species ; and 

 possibly some of the forms that I have kept apart as varieties may 

 have been independent species characterized by stronger differences 

 in limbs and other organs than their carapaces show. 



That this genus should have clearly preserved its peculiarities 

 during so large a portion of geologic time will not be disregarded by 

 those interested in the study of " persistent types " ; nor is it with- 

 out Entomostracan allies equally tenacious of generic independence 

 throughout the lapse of geologic time. "Where freshwater conditions 

 existed Estheria seems to have been often a ready comer. Probably 

 we shall have many other localities and horizons for it in the fossil 

 state as the little valves become better known to collectors *. 

 Of the wide distribution of the species, both in Palaeozoic and 

 Mesozoic times, we have clear evidence (judging from the carapaces, 

 and they appear to be distinct enough) in the occurrence of E. mem- 

 branacea in the Old Red Sandstone of North Britain and of Livonia 

 (900 miles apart); of E. striata ranging in the Carboniferous deposits, 

 from western Scotland to Silesia (900 miles) ; and of E. tenella, 

 with almost as wide a range -f, and passing upwards from the Coal- 

 measures into the Permian group. The apparently co-ordinal Leaia 

 presents almost indistinguishable carapaces in Pennsylvania, Fife- 

 shire, and Lancashire (through nearly 70 degrees of longitude), in the 

 lowermost and the uppermost Carboniferous deposits. Estheria minuta 

 is widely spread in certain strata of western Europe over a tract 

 measuring at least 600 miles from N.E. to S.W. ; but its variety 

 Brodieana is not known, it seems, out of Britain, where its southern 

 and northern localities are 400 miles apart %. E. Mangaliensis and 

 its representative in Bengal are upwards of 400 miles apart. E. ovata 



* They have hitherto been mistaken for various shells and for fish-scales, 

 t Much wider if E. tenella and E. exigua prove to be the same. 

 | E. minuta, var. Brodieana, has to be looked for in the Khatic beds at the 

 base of the Lias in the north-eastern counties of England. 



