1877. ] Geology and Paleontology. 693 
Calymene and Ceraurus. It will be remembered that the nature of the 
limbs of trilobites has been long a matter of controversy, some believing ` 
they had soft, membranous limbs, and others that they had jointed 
limbs, like those of the king crab (Limulus) and the fossil Eurypterus, 
etc., and still others that they may have had anterior ambulatory jointed 
limbs, and posterior broad membranous swimming abdominal append- 
ages. Mr. Walcott, after making many sections of trilobites, has discov- 
ered jointed appendages in them, numerous sections of Calymene senaria 
showing axial appendages with three joints; “the third joint in all ap- 
pendages of this species seen (seventy-seven in number) terminates in a 
round, blunt end.” In Ceraurus pleurexanthemus the limb is five jointed. 
The legs end in a single blunt end, and Mr. Walcott is inclined to think 
the legs will be found to have “ five or six joints with a terminal claw.” 
’ “ Attached to the basal (?) joint of the leg there is a slender-jointed 
arm of two, and probably three joints. Portions of pinnule are at- 
tached to the terminal joint. Whether they are branchial tubes cannot 
be satisfactorily determined from the section. In other sections rows of 
pinnule are shown which are undoubtedly branchial tubes. From the 
character of the remaining portion of the respiratory apparatus ao 
must have been attached to the arm. It is also quite probable tha 
branchia was attached to the basal joint of the arm. It may be rot + 
occurrence in this position in the section, is owing to a displacement of 
one of the branchiew attached to the side of the thoracic cavity. These 
branchiz are attached above the basal joint of the leg. The branchia 
in Calymene senaria projects out a short distance and then bifurcates, 
sending two spirals nearly to the edge of the dorsal shell. In some sec- 
tions the base appears to be a portion of the ribbon or band forming the 
spiral straightened out, while in others it is a closely coiled spiral. At 
_ the bifurcation the outer spiral springs from the base which continues on 
_ to form the inner spiral.” 
__ A transverse section of the head of Calymene cut so as to cross the 
hypostoma just within the posterior end, exhibited a space filled with 
cale-spar, which “ is the continuation of the visceral cavity of the thorax.” 
_ From the lower lateral margin of each side a jointed appendage extends 
_ Outward and downward. “ Between the upper pair of appendages and — 
= the glabella three pairs of appendages project. Their basal joint is slen- 
_ der, and, in two sections, closely resembles the maxillary joint of the leg 
_ Of the Eurypterus, modified in form, but undoubtedly subservient to the 
_ Same use as a part of the mouth.” Sections of Asaphus platycephalus 
: -furnish evidence that it had axial appendages of essentially the same 
_ Structure as those of Calymene and Ceraurus. 
Mr. Walcott concludes that the homology between the parts about the 
mouth of the trilobite and the same organs in the Hurypterida and 
Xiphosura is very direct and relates the families closely, and he consid- 
rs that the Xiphosura, Eurypterida; and Trilobita form the legion Me- 
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