82 



Guide to the Invertehrata. 



Crustacea, behind the head are narrow and small, hut broaden, out backwards 



GALLERY to the tail-plate, which is wide and fan-shaped. 



East Side. ^ fossil Squilla, Necroscilla Wilsom, occurs in the Middle Coal- 



Wall-cases measures of Derbyshire ; Pygocephalus Cooperi, from the Carbon- 

 iferous of Glasgow, may also belong to this division. True 

 Squillas occur in the Lithographic Stone of Solenhofen and in 

 the Cretaceous of the Lebanon (see wall-case) ; and Squilla 

 Wetherelli is found in the London Clay of Highgate (see Table- 

 case 85). 



2. — ScHTZopoDA. This division is represented to-day by forms 

 like Mysis, the " opossum-shrimp," characterized by the thoracic 



12-14, 

 Table- 

 cases 

 80-85. 



Fig. 142. — Callianassa suhterranea, Leach. (Living species.) 



feet being all "cleft-footed"; that is, having the exopodite and 

 endopodite present in each limb, a characteristic feature of the 

 adult Entomostraca, and of the larval state of many of the 

 Malacostraca. 



The cephalothoracic shield is smaller than in the true shrimps, 

 so that the gills are often left exposed on the bases of the thoracic 



Fig. 143. — C&Taipace oi &n Anthrapaleemon. Coal-measures: Staffordshire. 



legs. Some of the small Crustacea met with in the Coal-measures, 

 such as Falceocrangon socialis (Salter) from Fifeshire, probably 

 belong to this division. Udorella Agassiui, from the Lithographic 

 Stone, Solenhofen, is also a Mysiform crustacean. 



