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98 On the markings of the Carapar of Crabs. 
the same breadth that belongs to this lobe, the depression anterior 
to AL corresponding to the fissure between N and 'T. | So 2L (or 
3L, 2L) gives the breadth of the normal tooth or lobe N ; and 1L, 
when present, that of E. |. We thus find that usually when there 
are seven teeth anterior to S, each E, N, 'T', are doubled; when 
eight E, N are doubled, and either 'T' is trebled, or both 'T' and D 
are doubled. 
'T'he medial and antero-lateral areolets may be viewed relatively 
in two ways. lf we compare the medial region as a whole with 
either antero-lateral as a whole we find a resemblance in general 
form and subdivisions. Again we observe that the lobe 'T', 
areolets AL, 5L, 6L, 3M or 4M form a transverse zone across the 
carapax; again lobe N, areolets 2L, 3L, 2M constitute another 
transverse zone ; and lobe 1L; and 1M may be viewed as in another 
zone. 'lhese zones are often very distinctly brought out. "Phe 
lobes E and N are often a little posterior to the areolets adjoining, 
—or, the line of the lobe and these areolets has a direction a little 
obliquely back ward of a straight transverse line. Again, when the 
posterior prominent transverse line passes from the limit between 'T 
and S inward, anterior to 5L and not to 4L, as allüded to on the 
preceding page, the apparent zones are nearly straight transverse. 
The medial region in the Cancer group is usually narrower 
than the breadth measured between the outer angles of the orbits: 
but in the genus Cancer of Leach ( Platycarcinus, M. Edwards), 
ibis rather wider, owing to the smaller distance between the 
eyes. 'Phe depression limiting on either side this medial region 
terminates anteriorly in. the line of a fissure 1n the upper margin 
of the orbit between 1O and 20. : 
It is interesting to trace these regions in other families of the 
Brachyura ; but this we reserve for. another occasion. — Suffice 1t 
to say, that iu Atelecyclus, which is broader anteriorly than pos- 
teriorly, 3M is much elongated, 1P is as long. as broad, and there 
are the normal teeth with others intermediate. In Calappa in 
which the posterior part of the carapax is broadest, the medial 
region is comparatively small, and does not reach back quite to 
the middle of the carapax. 1P is oblong instead of transverse. 
In the Maiade, the medial region. is usually làrge, while the 
autero-lateral is very narrow anteriorly. "Phe prominent lateral 
spine or tooth corresponds to S and is usually far back of the 
middle of the side or margin, and often 1n the same line with. 1P 
(cardiac region of Desmarest). 4M is often obsolete.  'T'he 
deeper transverse depression, limiting the medial region behind, 
often, instead of extending outward to a point just exterior to S, 
(obliquely outward and backward in these Crustacea) extends 
more forward following the outline of the medial region and then 
bending outward along the depression between ll, and 2L, 3L, 
or between 2L, 3L, and 5L, 4L. In the former case the region 
of the tooth E; is anterior to the suture or depression, aud in the 
latter, the regions of both E and N. "l'races of the depression 
separating the antero-lateral and. postero-lateral regions. are also 
often apparent in this group. 
