Dr. E. von Martens on a new Species of Astacus. 359 
so-called active and passive states of the contractile action, 
Hence it results, from the comparison of the morphological 
properties and motory phenomena of muscular fibre and the con- 
tractile cortical layer of the Polythalamia, that the contractile 
substance during its action appears in two forms—the elongated 
(under certain circumstances cylindrical) form, in which the con- 
tractile particles are arranged with regard to a long axis, perhaps 
that of a cylinder; and the form of a plate or disk, in which 
the arrangement of the contractile particles has regard to the 
axis lying in the section of the cylinder. The contractile action 
itself is exhibited in the displacement of the contractile particles 
from one fundamental form to the other, and vice versd. Hach 
of the two principal or fundamental forms of the contractile 
substance in the animal organisms may be realized as the so- 
called active state, or as that of rest. In the muscular fibre the 
arrangement of the contractile particles with relation to the longi- 
tudinal axis of the cylinder is conceived as the state of rest, the 
discoidal form as the active form; while the reverse occurs in 
the Polythalamia. 
XLI.—On a new Species of Astacus. 
By Dr. E. von Martens. 
Tue Zoological Museum in Berlin has recently received from 
Dr. Richard Schomburgk a species of crayfish, almost equal in 
size to a lobster, from the Murray River, Australia. Dr. J. E. 
Gray, in a paper on the Australian Crayfishes, embodied in 
Eyre’s ‘Journal of Expeditions of Discovery in Australia,’ vol. 1. 
1845, p. 409, mentions a large species living in the said river, 
weighing about two pounds, and possessing the same flavour as 
the European lobster. This may be the same; but, as I could 
not find elsewhere a zoological description of it, I venture to 
regard and to describe it as new. 
Astacus armatus. 
Rostrum of the cephalothorax as long as the peduncles of the 
outer antenne, pointed, furnished on each side with four teeth, 
the posterior ones smaller ; its lateral edges continued backwards 
on a short extent of the cephalothorax in the form of a raised ridge. 
A single spine behind the middle of the orbit, somewhat behind 
the orbital edge, and continued backwards in a similar very short 
ridge. The sides of the cephalothorax, the hepatic as well as 
the branchial region, furnished with scattered conical spines, 
each enlarged at its basis, as if placed on a cushion. The lateral 
lamina of the outer antenne of the same spiniform shape as in 
Homarus vulgaris, but somewhat longer. Two strong spines on 
the interior edge of the carpus, the foremost much stronger. 
