THE CRETACEOUS PERIOD. 



267 



daris^ may be mentioned as being all important Cretaceous 

 groups. 



Coming to the Anmdose Animals of the Cretaceous period, 



Fig. iQi. — Galerites albogaleriis, viewed from below, from the side, and from above. 

 White Chalk. 



there is little special to remark. The Crustaceans belong for 

 the most part to the highly-organised groups of the Lobsters 



Fig. 192. — Discoidea cylindrica ; under, side, and upper aspect. 

 Upper Greensand. 



and the Crabs (the Macrurous and Brachyurous Decapods); 

 but there are also numerous little Osti'acodes, especially in the 

 fresh-water strata of the Wealden. It should further be noted 

 that there occurs here a great development of the singular 

 Criistaceous family of the Barnacles {^Lepadida), whilst the allied 

 family of the equally singular Acorn-shells {Balanidce) is feebly 

 represented as well. 



Passing on to the MoUusca, the class of the Sea-mats and 

 Sea-mosses (Polyzoa) is immensely developed in the Cretaceous 

 period, nearly two hundred species being known to occur in 

 the Chalk. Most of the Cretaceous forms belong to the family 

 of the Esc/ia7'idce, the genera Eschara and Eschai'ina (fig. 193) 

 being particularly well represented. Most of the Cretaceous 

 Polyzoans sue of small size, but some attain considerable di- 

 mensions, and many simulate Corals in their general form and 

 appearance. 



