PETALOCERUS BICORNIS. 275 
hid from view; the three basal joints are short; 
the two terminal ones subequally long, and 
furnished with a copious brush of strong cilia. 
These appendages are folded together and en- 
closed within the branchial chambers, where 
they, no doubt, fulfil the office of the flabella of 
the highest forms of crustacea; affording an 
interesting illustration of an organ being con- 
verted, by the force of circumstances, from its 
original purpose to the fulfilment of another, for 
which it was apparently most unsuited. 
PETALOCEROS BELLIANUS (Waite), Proc. Z. 8. 1856, 
p. 134.—Between tidemarks, Esquimalt Harbour. 
PETALOCERUS BICORNIS, N. 8.—Rostrum in duo cornua 
divisum habens. 
Carapace triangular, anteriorly produced into 
two horizontal hornlike processes, tuberculated 
with nodulated prominences all over the surface, 
but furnished with a series of large tubercles 
correspending in a line with the external margin 
of the carapace; the antero-lateral margin, con- 
stricted between the branchial and hepatic regions, 
furnished posteriorly to the orbit with two strong 
blunt processes, and posteriorly to the central 
constriction; armed laterally with two distinct 
narrow processes, and posteriorly with six closely- 
situated large round tubercles. 
r 2 
