A- 



1894.] NATURAL SCIENCES OF PHILADELPHIA. 397 



A STUDY OF THE SYSTEMATIC AND GEOGRAPHICAL DISTRIBUTION 

 OF THE DECAPOD FAMILY ATYIDJE Kingsley. 



BY ARNOLD E. ORTMANN. 



In the following paper I propose to give a revision of the family 

 Atyidce with especial reference to its geographical distribution. For 

 a true representation of the geographical range of a group of animals 

 it is necessary to examine the details of the distribution of all the 

 known species, as well as to define the systematic limits of each. 

 Every error in determining a species may be followed by great 

 confusion difficult to solve by subsequent investigation. In revising 

 the known genera and species it is necessary to state the relations 

 and affinities to each other in order to get an idea of the peculiarities 

 of the geographical distribution and to find out their cause. 



The family Atyidce, although a small one, comprises a consider- 

 able number of ill-defined species and genera, since most authors in 

 creating such did not investigate their relations to those already 

 known. In the typical genus Atya there are farther difficulties 

 due to the change of characters undergone by one species in the 

 different stages of life, which were wholly neglected by the majority 

 of authors. I have, notwithstanding, succeeded in revising the 

 family, pointing out the identity of certain species and genera, 

 defining some more correctly, and stating the affinities so as to leave 

 but a few species doubtful. I have determined a peculiar geo- 

 graphical distribution of the family agreeing well with its habits 

 and morphological characters. 



The family Atyidce is a very characteristic one among the Decapod 

 group of Eucyphidea. It shows on the one hand a number of 

 primitive characters, on the other a very peculiar shape of the 

 fingers of the chelae. As I have stated in a former paper, 1 the 

 Atyidce are closely connected with the family Acanthephyridce, which 

 live at great depths in the sea and contain, without doubt, the most 

 primitive Eucyphidea. The morphological differences between the two 

 families are the following: 1. The mandible in the Acanthephyridce 

 is furnished with a palpus (synaphipod), in the Atyidce it is wanting. 



1 Decapoden u. ScMzopoden der Plankton-Expedition, 1893, p. 42. 



