THE ENTOMOSTRACA 
OF 
THE CRETACEOUS FORMATION. 
Of the numerous microscopic organisms afforded by the disintegration of the 
Oolitic, Cretaceous, and Tertiary strata, whether calcareous, argillaceous, or sandy, 
the Polythalamia and the Entomostraca are by far the most abundant. The latter 
attract observation by their larger relative size, but have not been hitherto very 
extensively described. 
Our present observations are confined to the Entomostraca of the Cretaceous 
Formation, comprising the Chalk, Chalk-marl, Gault, and Greensand. The strata that 
have afforded the species herein described are the greensand beds of Blackdown 
(siliceous), of Warminster (calcareous), and of Farringdon (arenaceous) ; the Speeton 
Clay ; the Gault of Folkstone and of Leacon Hill, near Charing ; the Grey Chalk and 
Chalk-marl of Dover ; the Cretaceous Detritus of Charing ; the Red Chalk of Flam- 
borough ; and the common Wliite Chalk of the south-east of England. In the above- 
mentioned strata these little fossils lie about irregularly in all directions, and are not 
found in layers such as are often formed by the Entomostraca of the Wealden and 
Tertiary beds ; many are broken or eroded, and some bear evidence of having been 
crushed whilst in a recent state. The animal matter of the carapace is well preserved 
in the Gault specimens, and more or less so in others ; individuals bearing a trace of 
transparency and of original colouring occur, but are extremely rare, in the Chalk ; 
whilst in the Gault a large proportion remains transparent.^ The specimens generally 
occur as separate valves, but perfect carapaces are not unfrequently found, the latter 
condition being dependent upon the strength of the hinge attachment, which varies 
considerably in different species. 
The Gault and the Soft Chalk are very rich in Entomostraca ; but the most abundant 
supply of these and other Cretaceous animalculites is obtained from the “ Chalk- 
1 MM. Cornuel and Bosquet refer to the fact of the colouring matter being retained by some of the 
Entomostraca in the French Neocomian beds and the Maestricht limestone. 
B 
