Rhcztic Fossils. 1 6 1 



in its assemblage of forms, of the molluscan fauna of 

 the Caspian Sea, which is few in genera and species, 

 and of an abnormal kind, in consequence of the brackish 

 quality of the water. In the Black Sea also, there 

 are misshapen forms, stated by Edward Forbes to be 

 due to the gradual freshening of the water, because of 

 the constant influx of rivers into it, and the current 

 that runs through the Bosphorus into the Mediterranean 

 Sea. Both of these cases relating to continental seas of 

 a lake-like character, bear on the subject in question ; 

 especially seeing that these British beds of passage are 

 also comparatively poor in genera and species, and that 

 some of the species, to which special names have been 

 given, are variable or even distorted in form. Others 

 are hard to distinguish from shells common in the 

 Lias, while some also occur in the great Marine Bhsetic 

 series of the Continent, and some pass upwards into 

 the ordinary Lias. It is, indeed, difficult not to believe, 

 that some of these forms are in reality abnormal and 

 due to the locally unhealthy quality of the water in 

 which they lived. 



Though this volume has little to do with general 

 palaeontology, the following account of the fauna bears 

 on these questions, and I therefore give it in some detail. 

 It also helps to show that our Rhsetic beds represent a 

 set of local conditions that marked the passage of the 

 Keuper marls into the undoubted Lower Lias, and, 

 indeed, in places it is hard to separate them litholo- 

 gically. 



In these Khsetic beds there are now known two 

 Crustacea, viz. Tropifer Icevis, from one of the Bone 

 beds, and Estheria minuta, first known in the Keuper 

 sandstones, and one Brachiopod, Discina Toivnshendi, 

 the only one known in our Khsetic strata. Of the 



M 



