2 A REVISION OF THE ASTACIDA. 
= 
appendages of male transformed into styliform organs, or else absent ; 
external branch of posterior pair of appendages divided by a transverse 
suture; gills composed of a stem beset with numerous cylindrical filaments 
(trichobranchiz ), those borne on the proximal segments of the thoracic 
appendages (podobranchix) “imperfectly, or not at all, separated into a 
proper branchial and a lamellar portion; just in front of the base of the 
podobranchixe a pencil of long, fine sete (coxopoditic sete) arises from a 
small papilla on the proximal segment of the legs. 
Huxley has shown, in his essay “On the Classification and the Distri- 
bution of the Crayfishes,”’* that the family Astacidse, as defined above, 
naturally falls into two subordmate groups, to which I would assign the 
value of subfamilies, viz. : — 
1. The PoramoBuN®, comprising the crayfishes of North America, 
Europe, and Asia. In these the first abdominal somite in the male bears a 
pair of styliform appendages; +t the podobranchiz borne on the second and 
third maxillipeds and on the first three pairs of legs are furnished with a 
broad bilobed plaited lamina; the epipodite of the first maxilliped is desti- 
tute of branchial filaments; the coxopoditic setx are acute, not hooked, at 
the end; the telson is commonly divided more or less completely by a 
transverse suture. 
The subfamily Potamobiinze includes two genera :— 
a. Cambarus, distinguished principally by the absence of gills on the last 
thoracic somite and the absence of a bilobed lamina from the podobranchiz 
of the penultimate pair of legs, (Page 3.) 
b. Aslacus, characterized chiefly by the presence of a pair of branchiz 
on the wall of the last thoracic somite, and a folded lamina on the podo- 
branchiw of the thoracic appendages from the second maxilliped to the 
penultimate pair of legs inclusive. (Page 125.) 
2. The Parastacins, comprising all the crayfishes of the Southern 
hemisphere ; viz. those of South America, Madagascar, Australia, Tasma- 
nia, New Zealand, and the Feejee Islands.t In this subfamily the first 
abdominal somite is devoid of appendages in both sexes; the podobranchiz 
* Proc. Zodlog. Soc. London, 1878, pp. 752-788. 
+ The first abdominal appendages are rudimentary or absent in the female. 
{ In the collection of the United States National Museum there is a specimen of an undescribed Pa- 
rastacine from Colima, Mexico, collected by J. Xantus. This is the only representative of the Parastacine 
which has been found north of the equator. According to Huxley, op. cét., p. 771, there are two specimens 
of Paranephrops from the Feejce Islands in the British Museum, Perhaps the locality labels of the Mexican 
and Feejee specimens are erroneous. 
