S2 CRUSTACEA. 



5 CamtxM of Ma*rowra.~We have been thus minute in detailing 

 the** peculiarities of the Brachyura, in this place rather than in con- 

 nexion with our remarks on that order, because the subject has an 

 important bearing upon the homologies of the Macroura, as compared 

 with the Brachyura, to which subject we now allude. The ques- 

 tion is — 



What part of the carapax in the Macroura, corresponds to t/ie ventral 

 pieces (or mandibular) in the Brachyura? Milne Edwards observes, 

 that the epimeral suture in the former group crosses the carapax near 

 its middle; and that, therefore, the whole lateral and posterior por- 

 tions are the analogues of the ventral pieces, or the epimerals, as desig- 

 nated by him. This suture will be observed in several species figured 

 in the Atlas, and is particularly distinct in the genus Astacus. Milne 

 Edwards thus makes the larger part of the carapax epimeral in cha- 

 racter. 



Excepting that we consider what is here called epimeral, the man- 

 dibular segment, we agree with Edwards, for the most part, in the 

 above-mentioned deduction; so that, while the mandibular segment is 

 confined to the ventral pieces of the Brachyural carapax, it consti- 

 tutes its posterior half in the Macroura. 



On a hasty glance, w^e should hardly deem it probable that in 

 species so closely related as the Brachyura and Macroura, the same 

 parts should be so diverse. In the Scyllari, we may trace, on the sur- 

 face of the carapax, the medial, cardiac, and other regions of the 

 Brachyura, and in analogous positions; as though the surface had 

 similar relations throughout. We should little think the depression 

 between the cardiac and medial regions to be the course of a suture 

 between the mandibular and second antennary segments, any more 

 than it is so in the Cancroidea; yet below, there is a suture extend- 

 ing laterally from the anterior angles of the buccal area, which 

 evidently corresponds to the suture in Astacus that is continuous 

 across the back of the carapax in the line here pointed out. More- 

 over, there are no lateral pieces to the carapax. We are therefore 

 forced to consider this suture, although in the Macroura nearly bisect- 

 ing the carapax across, the same that takes a more backward course 

 in the Brachyura, and separates only the narrow ventral pieces. 

 There is no other suture of analogous character. 



It is an important fact, in its relation to this subject, that although 



