MUSEUM OF COMPARATIVE ZOOLOGY. 207 
River group at Cincinnati, Ohio.* The former compares with the leg 
o p ว P g 
as found in Ceraurus and the latter with the leg as restored in 
Calymene. 
Branchial Appendages. — The branchiæ have required more time 
and labor to determine their true structure than any of the appendages 
yet discovered. They were first regarded as small tubes arranged 
side by side, like the teeth in a rake; then as setiferous appendages, 
and finally as elongate ribbon-like spirals and bands attached to the 
side of the thoracic cavity, the epipodite being a so-called branchial 
arm. All of these parts are now known to belong to the respiratory 
system, but from their somewhat complex structure, and the various 
curious forms assumed by the parts when broken up and distorted, 
it was a long time before their relations were determined. 
The respiratory system is formed of two series of appendages, as 
found beneath the thorax. The first is a series of branchiæ attached to 
the basal joints of the legs, and the second, the branchial arms, or 
epipodites. 
The branchiæ, as found in Calymene, Ceraurus, and Acidaspis, 
have three forms. In the first they bifurcate a short distance from the 
attachment to the basal joint of the leg, and extend outward and down- 
ward as two simple, slender tubes, or ribbon-like filaments. In the 
second form they bifurcate in the same manner, but the two branches 
are spirals. These two forms occur in the same individual, but, as 
a rule, the more simple ribbon-like branchia is found in the smaller or 
younger specimens, and the spiral form in the adult. The exceptions 
to this, however, are such that it has little value for any comparison of 
structural features between the young and the adult. The first type of 
branchia is shown by Fig. 5, Plate I., Figs. 2 and 3, Plate IL, and the 
second, by Figs. 4-10, Plate IIT. The latter are very interesting, 
and a number of illustrations are given. The spiral structure is finely 
shown by Fig. b, Plate IIL, where, by the spiral being flattened, the 
plane of the section has passed through it so as to show the tube 
or ribbon as continuous and entire. Any of the sections, Figs. 4 — 10, 
clearly prove that spirals were cut across, although there is no con- 
nection between the segments except in Fig. 5. The bifid branchia 
is illustrated by Figs. 9 and 10, Plate III. The branchia on the left 
side of Fig. 3, and those of Fig. 8, Plate III., are formed of a finer, 
more slender tube or ribbon, and coiled in a larger spiral. The 
* Received from Mr, S, A, Miller and Dr. C. A. Miller, of Cincinnati, Ohio, 
