22 



FOSSIL ESTHERItE. 



Fig. 1. 

 Diagram showing 

 the relative posi- 

 tion of the Ridges 

 and Interspaces 

 in the shell of the 

 Estheria. 



other case is replaced by a modification of the ridges and broad intervening furrows, which 

 are squeezed up into rounded wrinkles (see woodcut, fig. 1). 



Not being as yet able to discern any essential difference between the 

 carapace-valves of the recent Estheria and the fossil from Kokenhusen 

 and from Caithness, I do not think that the generic term " Asmusia " is 

 required. 



I cannot find that the term " membranacea" (belonging to a Wealden 

 Cyclas) has been specifically applied to an Estheria of the Wealden, 

 though often misapplied in collections ; and I cannot substantiate the 

 remark I made on that point in 1859 (' Quart. Jom-n. Geol. Soc.,' vol. xv, 

 p. 406). The term "membranacea" remains, therefore, for R. Pacht's 

 species before us. 



Habitat of Estheria membranacea. — In the Estherian flagstones of 

 Caithness we have no evidence of any marine characters, nor does their 

 being associated with some thousand feet of sandstones and conglomerates 

 render it impossible that they themselves should have been formed in 

 fresh or brackish water. The occurrence of the fishes of the Old Red 

 series of Caithness in Russian deposits with marine shells does not neces- 

 sarily prove the marine nature of these Fishes, which may have had fresh- 

 water habitats, but have been hurried out to sea by floods ; or, indeed, 

 may have lived both in salt and in fresh water periodically. On 

 the other hand, the "traces of Lingula bicarinata," in the Estherian 

 sandy clay of Kokenhusen, point, at first sight, towards marine conditions. 

 They may, however, have been "derived" fossils — fragments washed out of some older forma- 

 tion ; or the Estheria may have been brought by flood or freshet low down the old estuary 

 towards the habitat of the Lingula; or the Lingula may have had temporary lodging 

 there whilst the sea held the estuary at times ; osE they may both have lived in brackish 

 water ; for we shall find further on, in the history of Lingula tenuissima of the Muschelkalk, 

 some evidence of its having become subjected to such conditions. The same may be said 

 for the fish-bed, with Lingula and " Posidonia," on the Dwina, mentioned by Helmersen 



(see p. 20). 



On the Toro-el (p. 20), fishes only are the associates of the "Asmusia;" and these 

 cannot be regarded, in the present state of knowledge respecting them, as direct evidence 

 either of the freshwater or the marine character of the deposit. In fact, their existing 

 congeners, whether Polypterids or Silurids, afi'ect lakes and rivers. 



a. Section of the 

 Eidges and Inter- 

 spaces in a fresh cara- 

 pace-valve. 



S. In some fossilized 

 valves, the Interspaces 

 are squeezed up, leav- 

 ing the Ridges in be- 

 tween. 



c. In other speci- 

 mens the Interspaces 

 are depressed when the 

 shell is crumpled, and 

 the Ridges are irregu- 

 larly upraised. 



Note.— Since Mr. C. Peach wrote to me in 1861 on the subject (p. 17), he has found Estheria mem- 

 branacea in three other quarries in the parish of Wick. The first is near the blacksmith's shop, Kilmster ; 

 the second is about a mile beyond this ; and the third is near the halfway-house between Wick and John- 

 o'-Groats. The distance between the first and last quarry is at least four miles, and this not in the line of 

 strike of the beds. Bipterus, Diplopterus, Osteolepis, Glyptolepis, and Coccosteus, with land plants, are 

 also found in these quarries. 



