1905.] * ORTMANN— AFFINITIES OF CAMBARUS. 95 
is easily conceivable that the increase of the number of hooks may 
_have taken place independently in different groups, and we shall 
see below that there is at least one case (C. pellucidus), where we 
are to assume an independent origin of an additional pair of hooks 
on the fourth pereiopods ; this is also rendered probable by the 
variability of this character seen in this species. That Faxon’s 
fifth group has developed an additional pair of hooks independently 
is clearly shown by the fact that here it is the second pair of pereio- 
pods that carries the additional hooks. 
Indications of a more general tendency to increase the number 
of hooks are found in occasional freaks in other groups ( C. propin- 
guus, C. virilis). 
General Shape of Carapace. —'The primitive type of the cara- 
pace seems to be more or less ovate, generally depressed. It 
assumes, however, sometimes a more cylindrical form (in some 
cave-species), and in some cases it is rather compressed. ‘The 
latter character is most remarkable in all burrowing species, and 
has developed independently at least in two groups (second and 
third of Faxon, gracitlis- and diogenes-groups). 
The Aveola seems to be originally rather broad and short. But 
there is a general tendency of it to become narrower, and at the 
same time to increase its relative length. This is evidenced in 
almost all groups, and a narrow, sometimes partly obliterated 
areola is found in species that have nothing whatever to do with 
each other. In fact, it is only the fifth group of Faxon where this 
tendency is not manifested. Generally, the length of the areola is 
correlated to the width, but there are exceptions. 
Rostrum. —'The shape of the rostrum is characteristic for most 
species, but it is available only as a specific character. The 
original type seems to be a rather long rostrum, with more or less 
parallel margins, with a marginal spine on each side, and a rather 
long acumen. ‘The chief tendency in further development is for 
the marginal spines to disappear, and for the whole rostrum to 
become shorter. This, however, is found in all five groups of 
Faxon in species which are not at all allied to one another. Even 
certain peculiar types of rostrum may reappear in a widely diver- 
gent group. Thus the 4/andingi-type is imitated, if the expression 
is permitted, by C. zmmunzs, and the burrowing species possess all 
a rostrum of similar shape. 
