| 96 On the markings of the Carapaz of Crabs. 
tral areolet, elongated anteriorly between the areolets 2M, the 
intra-medial ; AM, a transverse areolet just posterior to 3M, the 
post-medial. 'I'wodeep punetures usually rmnark the limit between 
3M and AM, even when there is no depression. 1M is annexed 
to the medial rather than the frontal region, because it more com- 
monly coalesces with the former, and is a part of it often in 
general outline. 
Antero-lateral Réegion.—In this region there are normally six 
areolets and they are often prominent :—1L, near the first tooth 
following the post-orbital. 2L, 3L, posterior to 1L, in a line 
nearly with the second tooth, and AL, 5L, 6L, between 4M and 
the third. tooth. 
Postero-lateral Region.—'This region on either side consists 
normally of 3 areolets 1R, 2R, 3R. 
Posterior Region.—1P is situated directly behind 4M and is 
often well cireumscribed, and sometimes in shape nearly like 3M 
reversed and shortened. 2P directly behind 1P, is sometimes 
simple, bt it is more commonly divided in the middle into two 
areolets. Behind these, is the posterior margin of the carapax. 
Orbital Region.—'The elevation which encloses the upper side 
of the orbit is usually divided by sutures into three parts. 
'he variations in the markings of Crabs arise in the main from 
the greater or less promainence of these areolets, their various sub- 
divisions, or their obsolescence. When ouly a few unculations 
are apparent on the carapax, a little study with. the normal type 
in view will commouly discover that the system is there although 
but just apparent ; and when once perceived a correct sketch is 
made without difficulty. 
In the obsolescence of the areolets, the posterior are the first to 
disappear, in which case this part of the surface 1s flat. Next the 
postero-lateral fail of being distinct. Next 5L and 6L coalesce, 
and also 1M and 2M. Next, the posterior of the medial areolets 
becomes obsolete, and at the same time 5L, 6L, disappear, or are 
indicated only by a slight undulation along the space that ordi- 
narly separates them.  ''he extra-medial may be only eircum- 
scribed anteriorly, and the slender elongation of the interno-me- 
dial 1s all that appears of that areolet ; next, the remaining antero- 
lateral areolets may disappear with the fronta!, and the surface 
is then quite smooth. 1L is sometimes indistinet when the other 
areolets are prominent, though usually it accompanies them. 
When 4L, 5L, 6L become indistinct, the transverse depression 
then proininent instead of passing behind them bends more forward. 
along 3M, and passes anterior to them, and so makes a different 
subdivision of the carapax in its general aspect and character. In 
another variety, the prominent transverse depression passes an- 
terior to 5L, but not anterior to 4L, (which may be obsolete,) and 
has nearly a straight course across the caràpax. 
In the subdivision of the areolets, the first that partake of it 
are 2M, 5L and 3M. A commeucement of this subdivision of 
2M (the extra-medial) is very common, and when completed it 
