1883.] NATURAL SCIENCES OF PHILADELPHIA. 45 



disposal of members who wish to have them. Tliey are fine robust 

 specimens, the larger ones measuring 6 inches in length by 3 inches 

 in height and almost 2^ inches in thickness. They were obtained 

 from a little pond occupying an old marl pit, near Clai'ksboro, 

 Gloucester Co., N. J. 



These mussels appear to be exceedingly prolific. The pregnant 

 females have the branchial uteri, as they have been appropriately 

 named by Dr. Isaac Lea, enormously distended with perfected 

 embryos. These appear with a cinnamon-brown shell, having a 

 conspicuous spinous tooth or hook to each valve, and are furnished 

 with long byssal threads. Wishing to ascertain the proportionate 

 amount of embryos, the followiug plan was adopted : — In an indi- 

 vidual 6 inches long the soft parts were weighed and found to be 

 135*44 grammes. The branchial uteri weighed 64 grammes and 

 the inner gills 7'34 grammes. Supposing the latter to be of the 

 same weight as the outer gills, free from embryos, this weight 

 subtracted would leave 56"66 grammes as that of the embryos, and 

 7 8' 7 8 grammes as the weight of the rest of the animal. In another 

 specimen in which the weight of the soft parts was 113'75 grammes, 

 the branchial uteri weighed 45*5 grammes, and the inner gills 5*2 

 grammes. Subtracting the weight of these would leave 40*3 

 grammes as the weight of the embryos, and 73'45 grammes for the 

 rest of the animal. In another specimen by weight, and counting, 

 the embryos in a milligramme were estimated to be 1,280,000. 



The mussels are infested with many water mites creeping about 

 among the gills. The young of the same, in various stages, were 

 observed imbedded in the mantle. The mite appears to be iden- 

 tical with the species Atax ypsiloijhot'ua, yfh'ich is a parasite of the 

 common mussel, Anodonta cygnea, of Europe. It was discovered 

 and described just 100 years ago, under the name Acarus ypsilo- 

 pho7-uH, by Dr. Christophori Gottlieb Bonz (Nova Acta Phys. Med. 

 Acad. C. L. C. Nat. Cur., Nuremberg, 1783, 52, Tab. I, figs. 1-4). 

 It is described and figured by Pfeiffer, with the name of Limno- 

 chai'es Anodontse (Naturg. deutscher land und siiss-wasser Mol- 

 lusken,. 1821, Taf. I, fig. 12) ; by Dr. Karl Ernst v. Baer, under 

 the name of Hi/drachne concharuin (Nova Acta, Bonn, 1826, 590, 

 Taf. XXIX, fig. 19) ; by P. J. van Beneden (Mem. de I'Acad. R. 

 des Sciences de Belgique, XXIV, 1850), and by Ed. Claparede 

 (Zeits. f. wiss. Zoologie, 1808, 445). 



Dl". Bonz's description, referring chiefly to the form, color and 

 marking of the mite, applies to ours ; and further he thought the 

 description of the details, of Claparede, applies sufficiently Avell 

 to the same. 



The characters of our mite are briefl}^ as follows :— ^ 



Bod}^ ovoid, black, with a sulphur-yellow median line, often 

 more or less interrupted, foi'ked in front, and ending in an angular 

 spot behind. The yellow marking divides the black into a pair 

 of lateral reniform spots and an anterior irregular lozenge spot. 

 Sides brown, from the eggs shining through. Head gray, with 



