202 OUR COMMON BRITISH FOSSILS. 



of modern times, we rarely lose sight of them. The 

 shales overlying the Coal-seams frequently look as if 

 somebody had sown millions of pins' heads there : 

 these are the fossil Cyprides^ allied to the water-fleas 

 seen in our modern ponds and tarns. Shales, slates, 

 and thin limestones not unfrequently owe their fissile 

 character to the abundance of Entomostracans of 

 various kinds. 



The large and beautiful Estheria — a form still 

 existing, and delighting in brackish water, and whose 

 two shells so much resemble those of a bivalve 

 mollusc (even in the recent state) that a young 

 student may easily be deceived into thinking he has 

 found another sort of animal — occurs first in the 

 Devonian rocks, and is also found in the Carboniferous 

 and Permian series. In the upper Trias of Warwick- 

 shire and Leicestershire it is not unfrequent ; indeed, 

 it is one of the few fossils found in these strata, which 

 are so rich in evidences of physical action — rain-drops, 

 sun-cracks, ripple-marks, etc. — and so poor in palseon- 

 tological souvenirs. 



To the naturalist there are few classes of the world- 

 wide (and also old world) group of Crustacea more 

 interesting than the Cirripedia, of which our modern 

 acorn-shells \Balanus), seen clustering after their 

 sessile fashion on the rocks, to the detriment of naked 

 feet when bathing — and the stalked kinds {Lepas) seen 

 attached to fragments of old wreck-wood which has 

 long been floating about and is at length cast ashore. 



