The most constant suture is one that runs along either sideviall, in a more 

 or less sinuous course, from the antero-lateral angle of the buccal cavern to the 

 postero-lateral angle of the carapace. This, which is known as the cjnmeral 

 fiuture, cuts off on either sidewall a ventral piece which may with much reason be 

 regarded as, in the main, the pleurum of the 4th or mandibular somite of the head. 



The cervical groove, which is so conspicuous in Nephrops, can generally he 

 made out, though obscurely, on the Brachyurous carapace. It is most distinctly 

 traceable in the Dromides. Wlien present, it helps to define the gastric region 

 of the carapace : its anterior loop is 2^i'obably represented on the Brachyurous 

 carapace by a groove that is sometimes found marking off a suborbital areola. 



Certain grooves or depressions are commonly noticeable which map out the 

 surface of the carapace into regions. The regions form three dorsal series — a 

 median and two lateral. 



The median series includes the frontal region, which lies between the orbits; 

 the (jastric region, which occupies the greater part of the middle of the carapace 

 behind the front and coincides in a general way with the boundaries of the 

 stomach ; the eardiac region, a small area which lies in the middle line imme- 

 diately behind the gastric region and indicates the position of the heart ; and the 

 intestinal region, which follows the cardiac and overlies the intestine just where 

 it curves over the endosternal apodemes to enter the abdomen. 



The lateral series include, on either side, the hepatic region, which occupies 

 the antero-lateral corner of the carapace behind the orbits ; and the hrancMal 

 region which takes up all the wing of the carapace outside the gastro-cardiac 

 region and behind the hepatic region. 



On the sidewalls of the carapace the triangular space on either side of the 

 buccal cavern is known as the pterygostomian region, between which and the 

 hepatic region lies the subhepatic region. 



Any or all of the dorsal regions of the carapace may be further divided 

 symmetrically into areolae. The gastric region is fairly constantly subdivided 

 into three areoliB — one of which is postero-mediau, the others being antero- 

 lateral. Again a narrow S23ace fringing the upper margin of the orbit is some- 

 times separated as the orbital region, while the space between the lower margin 

 of the orbit and the pterygostomian region is sometimes wide enough to be 

 distinguished as a suborbital region. 



Mention must here bo made of tlie linese anomtcricse, whicli though characteristic of the sub- 

 order of Anomura {Anortiala) are also found among the B/af/i//«m of the Hqmolidean families. 

 They are the homologues of the epimeral sutures of the Brachyuran carapace, but they are found 

 high up on the sidewalls of the carapace or even on the dorsum itself. 



7. Of the General Bionmiy of the Brachynra. 

 The majority of crabs are marine, but some live in brackish water, others 



