500 MEMOIES OF THE CARNEGIE MUSEUM 



(7. bartoni, diflfers from the rest ecologically as well as niorphologieally. It is dis- 

 tinguished by a number of characters, and there is no possibility of morphologically 

 intermediate foiuus, so that C. bartoni not only is a good species, but also belongs to 

 a different section of the subgenus. 



C. bartoni possesses in Penns3dvania a variety, C. bartoni robustvs, which, accord- 

 ing to my experience, is constant, and never runs into the typical form. It also 

 seems to occupy a slight]}' different territory, although oi'ten fuund associated with 

 the latter. These facts would justify us in regarding it as a good species. I have 

 not done so in the systematic part, since the facts at hand are too meagre to finally 

 decide this question. The range of (*. robiistas in Pennsylvania is only a small part 

 of the area occupied by this form, and in the states of Ohio, New York, and in 

 Canada, the conditions are entirely unknown. Furthermore a form similar to our 

 robtisttis, although, as it seems to me, not entirely agreeing with it, has been reported 

 from Virginia, Mar3dand, and Kentucky, and before particulars about the relation 

 of this form to C. bartoni and to our rolnitstns are known, we cannot judge as to the 

 taxonomic position of C. robustus. Therefoi'e I have refrained from modifying the 

 position hitherto assumed, that this form is a variety of C. bartoni. 



The other species of the subgenus Bartonius in Pennsylvania are G. carolinus, C. 

 monongalensis, and C. diogenes. They belong to the t7io(/enes-section, and all three 

 are closely allied. C. carolinus and 'monongalensis are more nearly related to one 

 another than to C. diogenes. The latter apparently is a more advanced form. 



C. carolinus and C. 'inonongalen.'<is are distinguished Ijy rather insignificant mor- 

 phological characters, discovered in the shape of the rostrum and the armature of 

 the chelipeds. But the difference in color is so striking that it is impossible to con- 

 found them in the field. Other cliaracteis also, although slight, hold good accord- 

 ing to my exj^erience, and I never have seen intermediate specimens. Moreover 

 the distribution of these two forms is ver}' characteristic, they being sharply sep- 

 arated topographically, and never being found associated at the same locality. Thus 

 all requirements leading us to pronounce them good species are met. Of course this 

 applies only to conditions in Pennsylvania, Maryland, and northern West Virginia ; 

 whether they are the same or different farther south remains to be seen. 



C. diogenes is more sharply separated from the species just discussed, and there 

 is no possibility of mistaking this species, more particularly as the color is markedly 

 different. But the morphological characters are also very nicely expressed, so that 

 in a case of a red (albinistic) specimen of this species I was not a moment in douljt 

 that I had to deal with ('. diogenes, and not with 0. carolinus, although the latter 

 was found associated with this form at this particular locality (Dunbar). There is 



