1862.] 



JONES FOSSIL ESTHER!^. 



141 



rarely any unmistakeable sea- shells associated with them in the 

 same bed ; and, when such do occur (as in the case of Lingula tenuis- 

 sima), the marine mollusk sometimes appears to have been dwarfed 

 by deteriorating influences. From what we know of the habits of 

 existing bivalved Entomostraca, it is probable that some degree of 

 saltness could be borne by Estherice, temporarily or continuously ; but 

 the recent Estherice (of which 22 species are known) have been mostly 

 found in rain-water pools and other fresh waters, and a few only 

 have been met with in brackish marshes, and none in the sea. So 

 also, of the allied Limnadia and Limnetis, their six or seven species 

 have all freshwater habitats. 



If living in lagoons communicating with the sea, the old Estherice 

 would have occasional marine companions; and those associated 

 shells that seem to have belonged to the sea from their supposed 

 relationship to existing marine mollusks may really have been in- 

 habitants of brackish water, or of more or less saline lakes. Where, 

 therefore, Estherice occur by themselves, or in the company only of 

 Fishes and Plants (as is often the case), it appears to me that they 

 may be regarded as having lived and died in fresh (or possibly 

 brackish) water. Where they are mixed with shells of presumed 

 marine habitat, they probably indicate either that they inhabited 

 brackish lakes having a quasi-marine fauna (such as the Caspian 

 Sea), or that fresh water was in close proximity to the place of 

 deposit ; or that they had lived in fresh water that had been perhaps 

 frequently replaced by the sea. 



The fossil Estherice will serve the geologist as useful indicators of 

 even transient changes of fresh- and salt-water conditions, either in 

 shallow water on coasts, or in inland lakes, where evaporation and 

 influx of rain-water, each varying in amount periodically, may have 

 produced freshwater, brackish, and saline deposits alternately. 



I refer to the * Monograph ' for full descriptions and illustrations, 

 and for copious references to the works of others on the subject. 



Table of the Fossil Estheriae and Leaiae*. 



Genus and Species. 



Locality. 



Estheria membranacea, 



Packt, sp. 



striata, Milnster, sp. 



, var. Tateana . . . 



, var. Beinertiana 



-, var. Binneyana 

 -, var. Beinertiana 



tenella, Jordan, sp. 



exigua, Eichwald, sp. 

 Portlockii, Jones 



Livonia; Caithness; Ork- 

 ney. 



Bavaria ; Belgium 



Berwickshire 



Silesia ; Lancashire ; La- 

 narkshire. 



Derbyshire 



Lancashire 



Lancashire ; Lanarkshire ; 

 France ( Autun) ; Sch- 

 warzwald (Murgthal). 



Saxony (Sal hausen ) 



Bussia (Orenburg and 

 Kazan). 



Tyrone, Ireland 



Geological Stage. 



Old Ked Sandstone. 



Lower Carboniferous. 

 Lower Carboniferous. 

 Lower Coal-measures. 



Lower Coal-measures. 

 Middle Coal-measures. 

 Upper Coal-measures, 

 or Permian. 



Lower Permian. 

 Permian. 



Permian. 



* Leaia is a problematical ally of Esfheria. 



