INTRODUCTION. 



and Anomurous Crustacea, distinguished so far as is necessary for my present purpose. 

 Their modifications in the Macrura will be 

 readily understood by reference to the dif- 

 ferent forms of that group. The example 

 I have here selected for the illustration of 

 this structure is Zozymus ceneus* which, 

 although exhibiting many still subordinate 

 divisions or lobules, which need not here 

 be designated, demonstrates with remark- 

 able clearness those points which I have 

 thought it requisite to describe, and is, 

 perhaps, as nearly normal as any one I 

 could have chosen. It is scarcely necessary 



to state that the foregoing descriptions are to be considered as belonging to the normal 

 form, and that there are to be found in be different species, variations of every part to 

 the greatest imaginable extent, always, however, preserving their mutual relations. 



When it is considered how numerous are the Crustacean fossils which exist in 

 the London Clay, and how plentifully many of the species are distributed, and the interest 

 which attaches to this class of animals, both on account of their general structure 

 and particularly of the relation in which they stand to the different formations in which 

 they are found, it is remarkable that so little attention has hitherto been paid to them, 

 and that so few species have ever been described. The crustacean inhabitants of the 

 earliest seas, indeed, have not been subject to this neglect, for the Trilobites have long 

 since been thoroughly studied, and have been made the subject of much philosophical 

 research and of many elaborate publications. The Chalk Crustacea of Great Britain have 

 also received a fair share of attention ; but those of the Eocene period have been almost 

 wholly neglected. In Professor Morris's 'Catalogue,' published in 1843, there are only 

 three species of Malacostracous Crustacea recorded as belonging to this formation, and for 

 the announcement and description of two of these we are indebted to a French naturalist. 

 Since that period there has been scarcely a record of an additional species, until a paper 

 by Professor M'Coy appeared in the 'Annals of Natural History,' in the year 1849,f 

 in which five additional species are described from the London Clay, preserved in 

 the Woodwardian Museum at Cambridge, and other collections. 



* In the figure, the following letters indicate the regions and principal lobes : f, the frontal region ; 

 o, the orbital ; H, the hepatic ; G, the gastric region ; Ga, the epigastric lobe ; Gb, the protogastric ; 

 Gc, the nasogastric ; Gd, the metagastric ; Ge, the urogastric. B, the branchial region ; Ba, the 

 epibranchial lobe ; B6, the mesogastric ; Be, the metagastric. C, the cardiac region ; Ca, the epigastric 

 lobe ; Gb, the metagastric. 



f On the Classification of some British Fossil Crustacea, with notices of some new forms in the 

 University collection at Cambridge, 'Ann. Nat. Hist.' 1849, pp. 181, 330, 392. 



