i9°5-] 



ORTMANN— AFFINITIES OF CAMBARUS. 9i 



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- 

 gi/us, 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, gracilis- and diogenes-groups). 



The Areola 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 d/andingt'-type is imitated, if the expression 

 is permitted, by C. immunis, and the burrowing species possess all 

 a rostrum of similar shape. 



