A CONTliriUJTrON TO A KNOWLEDGE OF THE FRESH- 

 WATER CJtABS OF AMERICA.— THE PHEIJDOTIIELPUU- 



siN^i:. 



By Maey J. Ratiibun, 



Second Asaietant Curator, JHviHion of Marine InverteVratee. 



INTRODUCTION. 



The critical study of the I'Meudothelphusinirs has led to somewhat 

 dincrcnt (joiurlnHions us to tlicir claHKiliciitiori and distribution from 

 those ])ublished by Dr. Ortmaiiii in his recjciit revision of the J'otainon- 

 ida;,' of whicli tlie Pseudotlielphusina! form a subfamily. The U. S. 

 National Musenm contains the larj^est colh'.ction of Pscnidotlielphusiiia; 

 in any inuseiun. Of tlie />'J species now inchided in the subfamily, .'55 

 are in tlie national collection, and are represented by 2.'i() specimens. 

 The material contained in several other larjje miisennis has also l)een 

 examined by the writer, includinjj type specimens of all species except- 

 ing Kpilobocera euhenftis Stimi)8on, PseudofhclphiiHa denticulata (Milne- 

 Edwards), P. w<fuatorialin (Ortmann), P. henrici Nobili, and liathbunia 

 fextw Nobili. 



Th(? comparison of this large amount of material seems to Justify the 

 division of the snbfamily into four f^enera: pHcudothdpkuHa, Potmno- 

 carcinuH, I'Jpilohocrra, and Haihhunia; and the evidence fjoes to show 

 that the species iidiabit comparatively restric^ted areas. The first part 

 of this paper is devoted to a (lcs(;ription of the sii))family, genera, 

 and new species, with analytical keys; the second part deals with the 

 distiibution of genera and sjjccies, (comprising all that is known at 

 present regarding the rang*; of these interesting forms. It should 

 not be inferred that the resnlts here published are in any degree (;om- 

 jdete. The need is felt of larg<;r series of specimens to deteimine the 

 extent of variation In eaeh species due to age and environment; there- 

 fore, in determining specimens the writer has refrained from undue 

 multiplication of specie's, and it is jmssible that some differ(!nces 

 which have been attributed to age or locality may later, with more 

 individuals for comparison, prove to be specific. 



' Zool. Jahrb,, Syst., 1897, X, pp. 29G-329. 



Proceeoinqs U. S. National Museum, Vol. XXI— No. 1168. 



507 



