Exploration of the Red River of Louisiana, in the year 1852 / by Randolph B. Marcy ; assisted by George B. McClellan. Page: 258 of 368

                                
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APPENDIX F.-ARACHNIDIANS.

The entire length, from  the tip of the chelicerae to the end of the
abdomen, is one inch and a quarter, the abdomen itself forming about
one-half of that length. The cephalothorax is composed of three distinct
segments; the anterior one much the largest, giving points of
attachment to the parts of the mouth, to the palpi, and the two anterior
pairs of legs; to the second thoracic segment is attached the third pair
of legs, and to the third segment the fourth pair. The anterior segment
of cephalothorax, seen from above, is subrhomboidal and smooth. At
its anterior margin are situated the two ocelli, separated from each
other by a deep groove. The chelicerse are very stout, and composed
of one single joint densely covered with setose hairs, and terminated
each by two spines, one above (finger of some authors,) rigid, and
another below (the thumb,) moving vertically against the upper. The
latter is compressed, acute, almost rectilinear, and smooth; the inferior
one is subconical, curved .upwards, acute towards the point, and provided
at its base inwardly with two spiny small processes. The palpi
are proportionally robust, stouter and longer than the three anterior
pairs of legs; somewhat shorter than the fourth pair, but of a stouter
appearance, as all the joints, four in number (the maxille excepted)
preserve the same diameter. They are covered on their whole length
with hairs similar to those on the chelicerae. The maxille are subtriangular,
provided only with brushes of hairs. The next joint (the joint
of the palpi) is very small and triangular; the second is the longest;
the third is the next in length; then the fourth, the tip of which exhibits
a minute smooth tuberculiform knob. The first pair of legs is
the most slender of the thoracic appendages, and about the length of
the third pair; the basal joint is quite short; the second is the shortest
of all; the third is the longest; the fourth, fifth, and sixth smaller in
the order enumerated. The last joint terminates like the palpi, bluntly.
This anterior pair of legs is called by some second pair of palpi, upon
the ground that their structure is most alike. The three remaining pairs
of thoracic appendages are seven-jointed, thus composed of one joint
more than in the first pair and palpi, and furthermore terminated by
two minute curved claws. The first, second, and third joints are short,
stoutish, and subequal; the remaining are longer and slenderer, the
fourth being the longest, and the other diminishing gradually. They
are covered upon their whole length with hairs similar to those which
cover the palpi, but perhaps less densely so. The abdomen is subovoid,
being a little depressed; it is densely hairy above and below, and composed,
as usual, of nine segments or annuli.
Collected on June the 10th.