25 Grud. 
CliUSTACEA. 
one (anterior) of the second maxilliped, and all those of the thoracic feet 
in Astacoides, are rudimentary ; pleurobranchiee are found only on the 
segments corresponding with th^ second, third, fourth, and fifth thoracic 
feet, they are entirely wanting in Cambarus, and are fully developed 
only in the segment corresponding to the fifth pair in the European cray- 
fish Astacns, s. strict., and Astacoides. The first maxilliped never 
has a well-developed gill, but in all subgenera it has a rudimen- 
tary appendage (epipodite) analogous to a podobranchia . Astacojjsis, 
CherapSy and Engceus have therefore twenty - one well - developed 
functionary gills, Paranephrops and Parastacus twenty, Astacus s. str. 
eighteen, Cambarus seventeen, Astacoides only twelve. On account of 
these differences and others in the development of the gills themselves, 
Huxley establishes two groups of freshwater crayfishes : — 
1. Potamohiidce. Apices of the podobranchiae separated into a 
branchial plume and a well-developed lamina ; no well-developed pleuro* 
branchia on the second, third, and fourth thoracic foot. .First abdominal 
segment bearing appendages, invariably in the males, usually in both 
sexes; telson usually completely divided by a transverse suture. Astacus 
and Cambarus, both belonging to the Northern Hemisphere. 
2. Parastacidce. Podobranchim with only the rudiment of a lamina, 
some of their branchial filaments hooked, the epipodite of the first 
maxilliped bearing a certain number of branchial filaments; pleuro- 
branchise of the second, third, and fourth thoracic foot present and well 
developed (except Astacoides). First abdominal segment without appen- 
dage in either sex. Telson never completely divided by a transvere 
suture. AstacopsiSy Cheraps, EngoeuSy Paranephrops, Parastacus, and 
Astacoides, all belonging to the Southern Hemisphere. 
He characterizes the 2 following new genera : — 
Parastacus, g. n., p. 771 : number of gills twenty, the same as in Para- 
nephrops, in other respects like Cheraps ; comprises the South American 
species Astacus brasiliensis and pilimanus (Martens). 
Astacopsis, g. n., p. 764: number of gills twenty-one, the same as in 
the two other Australian genera Cheraps and Engceus, but in other 
respects resembling rather Astacoides. Typical species, Astacus franklini, 
Australia. 
Homarus vulgaris, moult described by W. A. Lloyd, Field,^’ May 25th, 
1878; abstract, Zool. 1878, p. 226. 
[ Thaumastocheles (Wood-Mason, 1874)]. Astacus zaleucus (Zool. Rec. xi. 
p. 208), fully described by Willemoes-Suhm, Tr. L. S. (2) i. pp. 48-60, 
pi. X. fig. 1. Eyes and eye-stalks entirely wanting ; chelae very unequally 
developed ; eight spines at the squamiform appendage of the outer 
antennae ; genital opening of the male at the base of the third pair of 
feet. Sombrero Island, West Indies, 450 fath., red coloured. 
Thalassinid^. 
Gebia hirtifrons (Dana) from New Zealand ; Kirk, Tr. N. Z. Inst. xi. 
p. 401. 
