350 Dr. E.von Martens on a new Species of Astacus. 
The hands are exactly similar in size and in the shape of the 
teeth situated on the cutting-edges, both lateral edges of the 
hand serrated by blunt, short, conical spmes, bent foxy wards and 
forming a double row on the eal edge, and a single one on 
the internal. The femur of the four other thoracic feet furnished 
on its upper edge with two, three, or four spines. The upper 
face of the abdomen armed with strong conical spines disposed 
on each segment in a transverse row of six, the outer ones 
stronger ; only on the second segment, the lateral part of which 
is enlarged forwards as well as backwards, there are two outer- 
most spines, one behind the other, so that this segment possesses 
eight instead of six of them. The laminz of the abdominal feet 
membranaceous, with calcareous edges. The hinder half of all 
the lamine of the caudal fin soft and flexible; the lateral edges 
of the median one (the last abdominal segment) with a single 
tooth, further removed from its extremity than in the lobster, 
and corresponding in situation to the deep notch in this segment 
in the Crayfish. The two lateral pairs of caudal plates with 
the same transverse and denticulated suture as in the lobster. 
Length from the extremity of the rostrum to that of the 
caudal fin 330 millims. ; length of the hand 130 millims., breadth 
of the same 60 millims. 
Astacoides nobilis, Dana, from New South Wales, comes very 
near to this species in several respects, but is at once distin- 
guished by its blunt, almost toothless, rostrum ; its abdominal 
spines are much more feeble. The formation of the rostrum 
and the want of a deep notch in the caudal fin bring this new 
species nearer to Homarus than any other known species; but 
_the hands being equal, and the last thoracic segment being 
moveable independently of the cephalothorax, distinguish it from 
the lobsters. As I could examine one specimen ” only, which 
I did not wish to injure, the number of the gills could not 
be ascertained; and, as it is a female, there were no means 
of determining whether any appendages exist in the male 
These are the two characters on which is based the division 
Astacoides, adopted by Dana as a genus. Judging from 
some other characters, which are peculiar to Astacoides Ma- 
dagascariensis and the new species, as the prickles on the 
sides of the thorax and the membranaceous texture of the 
abdominal feet, I think it probable that also in the above cha- 
racters Astacus armatus will resemble Astacoides. Whoever 
may consider the teeth of the rostrum and the notches of the 
caudal fin to be generic characters will be under the necessity of 
establishing a new genus for our species. I prefer, however, 
to regard it as evidence against the generic value of those 
subordinate characters, the different combinations of which 
would not fail to require more and more new genera. 
