MUSEUM OF COMPARATIVE ZOOLOGY. 217 
DESCRIPTION OF THE SECTIONS, ETC. USED FOR 
TLLUSTRATION. 
PLATE 1. 
Fig. 1. Transverse section, perpendicular to the median axis, of the head of 
Ceraurus pleurexanthemus, on a line intersecting the eyes. The 
central lobe of the cephalic shield and hypostoma (h) entirely 
enclose the median cephalic cavity, which, in its present state, is 
filled with calespar. 
Fig. 2. A transverse section, cutting obliquely downward from near the pos- 
terior portion of the glabellar lobe to a point beneath, and a little 
back from the eyes. A ditsinct space occurs between the dorsal 
shell and hypostoma which is occupied by fragments of the mandu- 
catory appendages. 
Fig. 3. This section is taken a little posterior to the preceding, and terminates 
beneath, farther back. The cephalic appendages are shown only 
near their bases. 
Fig. 4. This is one of the most satisfactory sections obtained of the cephalic 
region of this species. In this and the three preceding, the ap- 
pendages have been, apparently, crushed back between the hypostoma 
and dorsal shell, so as to give an incorrect idea of their true position 
when seen in the sections. In Fig. 4 the jointed appendages are 
indicated, and also the manner of their arrangement, the leg on the 
left side showing three joints. This would hardly be intelligible 
were it not for the sections of the species next to be mentioned, The 
four sections taken to illustrate the head of Ceraurus are among 
many that show similar features in about the same condition of 
preservation. The branchiæ shown in Figs. 3 and 4 are not consid- 
ered cephalie, but as thoracie, and pushed beneath the cephalic 
shield after the death of the animal. 
Fig. 5. A section of the head not far from the position of that illustrated by 
Fig. 4, but by reason of the enrolment of the animal, portions of the 
thoracic appendages are cut across, and, as mentioned of Figs. 1-4, 
the latter have also been forced beneath the head. One of the most 
interesting features of this section is the ribbon-like branchiæ, b, b. 
The appendage o is probably cephalic ; all others, thoracic. 
Fig. 6. With this section we commence a series of five cut from different in- 
dividuals of the species Calymene senaria. All show the cephalic 
appendages. Without exception they are cut transversely and 
obliquely down through the head from just back of the posterior 
segment to the lower anterior side, intersecting the hypostoma (h) 
towards its posterior end. The posterior or fourth pair of appen- 
