BULLETIN OF THE 
PLATE III. 
Fig. 1. Transverse section of an enrolled Calymene, cutting across the upper 
posterior margin of the head and the anterior upper side of the 
thorax in such a manner as to remove a portion of the dorsal shell 
and contents of the visceral cavity, laying open the visceral cavity 
and the basal portion of several thoracic appendages. These are 
setiferous, a condition not observed in any other section. But one 
side of the section shows the structure, as shown in the figure ; the 
other was destroyed in cutting, and the drawing is made to show 
the two sides from the data given by the right side. 
Fig. 2. Transverse section of the upper side of the head and the anterior 
portion of the thorax of an enrolled Ceraurus. The central 
cephalic cavity is shown and also portions of the cephalio appen- 
dages. The upper side cuts across the thorax and the peculiar 
branchi are shown, the one on the right side having been pushed 
out of its normal position. A branchiæ, or branchial support of 
the same character, occurs in a section of Acidaspis Trentonensis 
and in the same position, i. e. in association with the anterior 
thoracic appendages, these organs may not have performed the 
respiratory function, but acted as the support of more delicate 
branchial filments or lamella, all traces of which are lost. 
Fig. 3. Transverse section of a Calymene cutting across the head from the 
Figs. 4-6. 
anterior side back to the lower posterior margins and thence 
across five segments of the thorax as the shell was enrolled. The 
basal joints of the legs are shown, and also the branchial apparatus. 
On the right side the latter has the usual appearance as seen in most 
sections of this species, but on the left side a variation is observed. 
The ribbon forming the spiral is very fine and closely coiled. 
'The parts seen in Fig. 8 are of the same nature. The base is 
attached to the basal joint of the leg, but, owing to the section not 
being exactly transverse, this is not beneath the same segment as 
the basal joint on the right side. "The combination of the two 
forms of branchiæ in this section and the presence of another 
variation in Fig. 2, a section from the same species, proves that 
variations existed in the thoracic branchial appendages. 
Longitudinal sections of Cerawrus with the branchiæ preserved, 
In none of these are the branchiæ in a normal position. In 
Fig. 5 they have been forced into the cephalic cavity, and the 
section cuts across the spinous extension of the pleure. Frag- 
ments of the legs are mingled with the branchiæ in the upper 
portion of the figure, but in their extension downward the spiral 
form is finely preserved. It appears as though the mass of the 
viscera, etc. had beén forced towards the head, and that five of 
