52 REPORT — 1875. 



into parts that are not constant, and when present do not represent any In- 

 ternal organization, as he has done in dividing the branchial region into : — 

 epibranchial, or anterior division of the branchial region ; the mesobranchial 

 and metabranchial divisions, which consist of lobes variable in form, but 

 represented in most genera by a smooth surface. 



The cardiac region he divides into an anterior and posterior portion. The 

 anterior alone represents the position of the heart ; the posterior represents the 

 part that lies between the heart and the posterior margin of the carapace. 



The hepatic regions he does not subdivide, but circumscribes their limits 

 within the extent of the internal organ — an object of consideration, as it 

 appears that the extent of this organ is one of the most important features 

 in the moulding of generic forms. The other regions are those situated on 

 the ventral sui'face, and which will be considered in a future Report. 



The value of a clearly defined knowledge of the various markings that are 

 represented on the dorsal surface of the carapace of Crustacea is best appre- 

 ciated in the study of fossil specimens, where the remains of animals, how- 

 ever well preserved, can be read by their external features only. 



It is therefore with a view to accelerate this that I liave in this Report 

 endeavoured to lay down the several regions that are represented by the 

 markings exhibited on the surface of the carapace. 



Taking advantage of the information conveyed by studying the labours of 



the previously mentioned eminent carcinologists, I have laid it down as a rule 



for guidance, that the external markings must define the internal structure ; 



and where this is not the case the lobe or projection exists as an excrescence. 



The most important and constant divisions are :— 



The anterior, which lies immediately above the antero-cesophageal gan- 

 glion. This may readily be subdivided into the orbital and antennal portions. 

 The entire region, from its relation to those organs from which alone intelli- 

 gence is derived, may be termed the cephalic region. 



Directly posterior to the cephalic region is the gastric ; this is generally 

 very conspicuous, the intensity of the jjostero-lateral markings being rendered 

 more distinguishable by the inner surface of the carapace being adapted for 

 the attachment of the anterior tendon of the mandibles. 



The stomach consists, in the more perfectly developed types, of a large 

 central chamber, the form of which not only varies in genera, but is capable 

 of extension and of being collapsed in the same individual. It has also 

 antero-lateral cavities and a posterior or pyloric extension ; but these are 

 produced at a lower line, and therefore liable to be less conspicuously repre- 

 sented on the dorsal surface. 



The lobe which M. Milne-Edwards has termed the mesogastric, corresponds 

 with that portion of the stomach that is projected above the gizzard-like 

 plates that stand at the entrance of the pyloric chamber. 



On each side of the pyloric or mesogastric lobe are two generally well- 

 defined .lobes that correspond, and are probably induced by the presence 

 beneath of the genital apparatus in the male and the commencement of the 

 ovaries in the female. I think, therefore, that it is desirable to retain 

 for these lobes the name that was first bestowed upon them by Desmarest, 

 and call them the genital regions. 



Posterior to these comes the cardiac region, which corresponds very closely 

 with that of the heart, which lies immediately beneath it. 



Posterior to the heart the carapace protects no distinct viscera ; but the 

 posterior margin covers the anterior half of the first somite of the pleon. 

 The muscular system which moves the pleon is attached to the apodema that 

 divides tlic cardiac from the branchial cavities, which also affords attachment 



