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On the markings of (fie Carapaz of Crabs; 95 
Anr. XIL—On the markings of |the Carapax of Crabs; by 
| 
d 
Jaues D. Dana. 
'luE areas into which the surface of the carapax of Crabs is 
subdivided were imperfectly distinguished and named by Desma- 
rest. '"l'hisauthor designated the regions according to the internal 
parts which they covered. But there is a system in the mark- 
ings which this mode of indicating does not express, and more- 
over there is a uniformity of character and number which it fails 
to exhibit. Had the uniformity of number, position and outline 
been generally recognized, the drawings in this department of 
Crustacea would not be so commonly incorrect ; for even figures 
from high authority usually misrepresent the character of the 
surface, and few can be pointed to that are faithful sketches. 
Moreover these regions, correctly understood, indicate certain ho- 
mologies in the skeleton of the Decapods. We propose at this 
time simply to describe the surface markings as they appear. 
The above figure (fig. 1,) shows the normal number and 
position as observed in species of the Cancer group. —. A depression 
crosses the carapax just back of the middle, and terminates 
anterior to the last of the normal lateral teeth. — Another depres- 
sion begins in this line either side of the middle and extends 
towards the eyes. "'l'hese depressions divide the carapax into a 
medial region, two antero-lateral regions, and a posterior region. 
From the medial, we exclude a frontal portion as a frontal region, 
besides also an orbital ; and from the posterior two postero-lateral 
regions. Each region has its several subdivisions or areolets. 
. In the figure referred to, the areolets of the frontal region are 
marked F'; of the orbital, O ; those of the medal, M ; those of the 
posterior, P; those of the amntero-lateral, L; and those of the 
postero-lateral, &;—R being the initial of the last, syllable in 
the word lateral, while L. is the initial of the first. 'Pl'he minor 
subdivisions correspond to prominences or tubercles of the surface 
aud are normally as follows :— 
F'rontal Resgion.—1F' the front margin; 2F a prominence 
just posterior to the front either side of the middle. 
Medial R'egion.—1M, two small anterior prominences, the pre- 
medial; 2M, two large areolets the eztra-medial; 3M, a cen- 
SzcoNp Sxnrmzs, Vol. XI, No. 31.—Jan., 1851. 12 à 
— 0 cs MR cic f 
