46 . PROCEEDINGS OF THE ACADEMY OP [1883. 



dumb-bell eye-spots. Limbs gray, translucent, with the chitinous 

 investment bluish black, hirsute, ending in pairs of double falcate 

 ungues. Terminal joint of the palps ending in three minute 

 uncinate denticles. Anal plates of the females usually with about 

 18 to 22 acetabula to each. Length of body 1-375 fo 1-75 ram., 

 breadth 1-125 to 1-5 mm. Inhabits the branchiae and mantle of 

 Anodonta Jiuviatilis. 



The colors depend mainly on the contents shining through the 

 transparent chitinous investment, which under reflected light 

 exhibits a bluish-black tint. Commonly the black color is intense ; 

 and in alcoholic specimens the whole body is black. In several 

 individuals the black passed into a chocolate hue. Dr. Bonz 

 describes the European mite as black, with the median dorsal 

 mark pale yellow ; Pfeiffer as red-brown with a citron-yellow 

 mark, and Beneden says it shows a Y in white, from which it was 

 named. 



The number of acetabula to the anal plates is variable ; in one 

 mite he found 23 to each plate, in a second 22 to each, in a third 

 22 to one and 17 to the other, and in a fourth 18 to one and 17 to 

 the other. Claparede gives from 15 to 20 as the number to each 

 plate in the European mite. 



The variations of our mite, from the characters given of the 

 European mite, ai-e such as occur among individuals of either, and 

 he therefore saw nothing distinguishing ours as a diflerent species. 

 Claparede describes another mite which infests the European 

 Unios, which he distinguishes under the name of Atax Bonzi. The 

 speaker had also observed a different mite, infesting the common 

 mussel, Unio complanatus,, of the Delaw-are River; of this mite he 

 exhibited a drawing made in November, 1854. He suspected it 

 to be the Atax Bonzi; but the question can only be more positively 

 answered after the examination of certain details, which he hoped 

 soon to have the opportunity of making. 



If our two parasitic mites are identical with those of European 

 mussels, it not only makes it appear probable that they are of 

 common origin, but renders it the more probable that this is like- 

 wise the case with their hosts, even if these are not I'egarded of 

 the same species. 



Professor Leidy also exhibited a collection of bod3'-lice, 

 Pediculus vestimenti, from Jews of Odessa, Russia, presented by 

 Dr. A. G. Stratton. They range in size from 1-25 to 3-875 mm. in 

 length, and appear in no respect to differ fi'om those found on 

 natives of our own country. 



The Ice of the Glacial Period. — Professor Heilprin, referring 

 to the subject of glaciation, stated that in his opinion the vast 

 sheet of ice Avhich is generally supposed to have covered during 

 the great ice age a considerable portion of the northern regions of 

 the European and North American continents, could not have had 

 its origin, as is maintained by most geologists, in a polar " ice-cap," 



