INTRODUCTION. ili 



by M'Coy the nuchal furrow, and by Milne Edwards " le sillon cervical." It passes in 

 a very uneven line behind the hepatic region, backwards by the side of the metagastric 

 lobe and across behind the urogastric. Thus the anterior portion to which Professor 

 Edwards gives the name of cephalic arch ("arceau cephalique") consists of the frontal, 

 the orbital, the gastric, and hepatic regions ; and the posterior portion, the scapular arch 

 ("arceau scapulaire"), is formed of the branchial and cardiac. 



I take the normal form of the Brachyurous carapace (to which for the present 

 I confine my attention) to be that in which the regions and their secondary divisions 

 or lobes are more or less distinctly marked by furrows, and the latero-anterior margin 

 furnished with five processes, including the extra-orbital process, in the form of spines, 

 teeth, or tubercles. This will be sufficient for my present purpose, and it would only be 

 involving an unnecessary and ambiguous discussion to enter, in this place, into a more 

 intricate subdivision of the regions. 



In the normal form of the Brachyurous carapace there are, according to the system 

 which I here adopt, nine regions. Of these three are single, placed on the median line, 

 and three pairs, which occupy the lateral portions of the carapace. The azygos regions 

 are the frontal, the gastric, and the cardiac ; the pairs are the orbital, the hepatic, and the 

 branchial. The frontal region is placed at the anterior margin, and is generally very small 

 in the typical Brachyura ; but in the Oxyrynchi and in most of the Macrura and several 

 of the Anomura, it is developed into a more or less projecting rostrum. It is circumscribed 

 behind and above by the gastric, and laterally by the orbital regions, and beneath 

 it ordinarily joins a projection of the epistome, and covers the antennules or internal 

 antennas, forming the upper vault of the antennary fossae. The orbital region on each 

 side is also small, and occupies the anterior margin of the carapace from the frontal to the 

 hepatic regions, and it is bounded behind by the broad anterior margin of the gastric, 

 from which it is generally distinguished by a slight elevation. It is often armed with 

 a spine or tooth or tubercle on its inner and outer angle, the latter forming the first of the 

 five normal projections of the latero-anterior margin of the carapace. The gastric region 

 occupies, in most cases, a very extensive portion of the anterior half of the carapace, 

 extending at its anterior margin along the whole breadth of the frontal and orbital regions ; 

 it is bounded laterally by the hepatic and branchial, and posteriorly by the anterior 

 (epicardiac) lobe of the cardiac. It is divided into lobes which are more or less distinct 

 and prominent, in some cases being almost as strongly distinguished from each other 

 by grooves as the regions themselves, in others altogether confluent, and scarcely 

 recognizable by slight elevations. The anterior pair (epigastric), which are in contact with 

 the frontal, and in some cases extending to the orbital regions, are very small and 

 ordinarily inconspicuous ; the next which are termed protogastric are very large, and 

 occupy the greater part of the area of the gastric region ; the union of this pair of lobes w 

 often interrupted by an elongated projection of the next lobe, the mesogastric, which 

 is placed in the mesial line, and is identical with what was formerly called the genital 



