iv INTRODUCTION. 



region ; the metagastric lobes are placed behind those hitherto mentioned, and generally 

 meet on the mesial line, behind the mesogastric, becoming confluent ; the posterior lobe of 

 this region is called the urogastric, and often consists of a mere narrow, transverse line, 

 sometimes confounded with the anterior, although, in other cases, it is as long as it 

 is broad, and quite readily distinguished. The hepatic region is somewhat triangular, and 

 occupies externally the anterior part of the latero-anterior margin, from the orbital to the 

 branchial; it is bounded on its inner side by the protogastric lobes, and behind by 

 the epibranchial ; in those cases in which the margin is furnished with the normal number 

 (five) of processes, the hepatic region has the second and third allotted to it. This region 

 is, in many instances, confluent with the gastric and branchial, but in others the limiting 

 furrow is sharp and distinct, and constitutes a portion of the sulcus cervicalis, which 

 divides the cephalic from the scapular arch, as before described. The cardiac is the 

 posterior mesial region, and answers to the cardiac and intestinal regions of Professor 

 Milne Edwards's former arrangement, and to the " cordiale " and " hepatique posterieure " 

 of Desmarest. It is bounded anteriorly by the urogastric lobe, laterally by the 

 metabranchial, and posteriorly forms the posterior margin of the carapace. It is composed 

 of two portions, named by M. Edwards the anterior and posterior lobes, but for which 

 I propose the names respectively of epi- and meta-cardiac. The branchial regions 

 are very large, occupying in most cases the moiety of the area of the carapace ; and 

 in some, particularly of the triangular forms, even much more. Externally, it forms the 

 posterior half of the latero-anterior and the whole of the latero-posterior margin of the 

 carapace. Its anterior boundary is the hepato-branchial portion of the cervical furrow, 

 and the inner the gastro-branchial and cardi-branchial furrow. It is divided into three 

 tolerably distinct parts, termed the epi-, the meso-, and the meta-branchial lobes. 

 The first of these extends across the lateral portion of the carapace from the lateral margin, 

 the fourth process of which, when it exists, essentially appertains to it ; the inner margin 

 usually coincides with the meta- and uro-gastric lobes. The meso-branchial lobe I 

 propose to limit to a much smaller area than has been assigned to it ; an area which is in 

 many genera so clearly defined as to involve, I think, no ambiguity. It is commonly 

 a triangular or rhomboidal space, embracing the fifth marginal tooth, and extending 

 but a short space inwards between the epi- and meta-branchial lobes. The latter is 

 a broad space, forming nearly half of the whole branchial region, and it frequently presents 

 a surface of so different a character from the rest of the carapace as to be readily 

 distinguishable. This will be found very strongly marked in the genus Bromilites, and 

 particularly in that species to which Desmarest gave the name of Inachus Zamarckii* 

 Such appear to me to be the essential divisions of the carapace in the Brachyurous 



* So striking is their structure in the species in question, that Mr. M'Coy considered it as the principal 

 character on which he founded his genus Basinotopus (now referred to Dromilites), which also suggested 

 the name. He, however, appears to have failed to ascertain its true character as the modified meta-branchial 

 lobe. 



