502 GEOFFREY SMITH. 
living and fossil. There is no trace of an extra segment in 
the posterior part of the thorax, which has been supposed to 
be present in the Huphausiide. 
(c) Appendages. 
The first antenne in all the Syncarida present a very 
uniform structure ; there is a three-jointed peduncle with two 
flagella attached. In all the lving forms, and probably in 
Preanaspides, there is a definite flexure between the second 
and third joints; this flexure does not appear in the fossil 
Gampsonyx and Paleocaris. In all forms, except 
apparently Gampsonyx, the inner flagellum is very much 
TEXT-FIG. 5. 
a 
otocyst. SS 
= a 
Koonunga cursor. First antenna. 
shorter than the outer; in Gampsonyx the two flagella 
appear to have been of equal length. 
In all the living forms an auditory organ has been dis- 
covered upon the upper surface of the basal joint of the 
peduncle of the first antenna. This organ is roughly oval in 
Paranaspides and Koonunga, kidney-shaped in Anas- 
pides. 
It consists of a hollow sac opening on the dorsal inner 
surface of the basal joint of the first antenna by a narrow 
transverse slit. ‘he hollow of the sac is filled with fluid, but 
there are no solid concretions of any kind. On the outer wall 
of the sac is a row of club-shaped chitinous rods, arranged in 
a single antero-posterior series. If we study the histology of 
the sac by means of a transverse series (Pl. 12, fig. 1) we see 
