220 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 vnsceral 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 cephalic appen- 

 dages. The upper side cuts across the thorax and the peculiar 

 branchiae are shown, the one on the right side having been pushed 

 out of its normal position. A branchiae, 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 fmiction, but acted as the support of more delicate 

 branchial filments or lamellae, all traces of which are lost. 



Fio'. 3. Transverse section of a Calymene cutting across the head from the 

 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 branchiae 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. 



Figs. 4-6. Longitudinal sections of Ceraurus with the branchia) preserved. 

 In none of these are the branchioo 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 pleurae. Frag- 

 ments of the legs are mingled with the branchiae in the upper 

 portion of the figure, but in their extension do-wnward the spiral 

 form is finely preserved. It appears as though the mass of the 

 viscera, etc. had been forced towards the head, and that five of 



