224 
BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 
the sections described have been used, and also confirmatory evi- 
dence from many other. On Plate I. figs. 6—10, we have the 
strongest evidence of the arrangement and structure of the cephalic 
appendages. The large basal joints of the fourth or posterior pair 
are shown in all,as also more or less of the three anterior pair. 
If the student will take a specimen of Calymene senaria, or an allied 
form nearly detached from the rock, and study it as he examines 
the illustrations of the sections and restorations of that species, he 
will see how, in cutting across such appendages as are shown in the 
restoration, he would obtain sections like those figured on Plate I. 
figs. 6-10. The position and form of the thoracic legs are taken 
from such sections as represented on Plate III. fig. 9, Plate V. figs. 
1-4, and. Plate II. fig. 10, as also the confirmatory evidence of po- 
sition in Plate IL. figs. 1-3 of Ceraurus. The more cylindrical 
character of the legs of Calymene as compared with those of Ce- 
raurus is shown in Plate IL. fig. 10, and in Plate V. figs. 1, 3, 4. 
The character of the appendages beneath the pygidium is not as 
well known ; many sections show their presence as far as one, two, 
or three joints, but beyond that their form is unknown. They 
are restored as jointed to the end as beneath the thorax. There 
is reason to think that some of the anterior appendages may have 
been modified in their terminal joints, as also the posterior appen- 
dages. Of the character of these modifications, if they existed, 
future investigation must enlighten us. The rough appearance 
given to the inner end of the large basal joints of the posterior 
pair of cephalic legs is the result of an attempt of the lithographer 
to change the form of the joints, and not designed to be so in the 
restoration. 
Fig. 2. A transverse thoracic section of Fig. 1. In this there is given a view 
of the structure of the thoracic appendages as they appear from à 
study of the sections. The position of the intestinal canal, the 
cutline of the ventral membrane or ventral surface, and the char- 
acter and position of the appendages, with the exception of the 
terminal joints of the legs, have been seen as represented. The 
spiral bifid branchiæ and branchial arms are seen in Figs. 9 and 
10, Plate III. There are two other forms of branchiæ known in 
Calymene. One is shown in Plate III. figs. 3 and 8, and another 
in Plate I. fig 8. 
Fig. 3. Transverse section of the thorax of Ceraurus pleurexanthemus, to show 
the character of the legs. The branchiæ are not attached, al- 
though the sections shown by Figs. 1, 2, and 3, Plate IL, would 
fully warrant their restoration. 
Fig. 4. The jointed legs figured by Eichwald. 
Fig. 5. Jointed legs found on a slab of limestone associated with Trilobitic 
remains, From Cincinnati, Ohio. 
