Genth.J 30 [Oct. 2, 



of the right-hand series largest and most numerous ; marginal seta? large, 

 lamelliform, obliquely truncate, projecting beyond the right-hand body- 

 margin, the posterior ones continued across the posterior part of the dorsal 

 aspect ; peristome- field extending to the center of the ventral surface, the 

 left-hand margin with a series of fine par-oral cilia, the right-hand border 

 ciliate and bearing a membrane ; contractile vesicle single, spherical, near 

 the center of the left-hand border ; nucleus single, large, ovate, in the 

 posterior body-half ; anal aperture postero-terminal ; dorsal surface bear- 

 ing numerous long hispid hairs in longitudinal lines and three large vibra- 

 tile setae developed anteriorly. Length of body, 1-145 inch. Habitat. — 

 Marsh water, with Sphagnum. 



Contributions from the Laboratory of the University 

 of Pennsylvania. 



No. XXIV. 



CONTRIBUTIONS TO MINERALOGY. 



By F. A. Genth. 



{Bead before the American Philosophical Society, October 2, 1SS5.) 



During the last two or three years numerous mineralogical observations 

 have been made, some of which I had intended to investigate more fully, 

 but, as I fear that the time which this would require would delay, if not 

 altogether prevent their publication, I give in the following the more in- 

 teresting : 



1. Tin, and associated Minerals. 



A highly interesting occurrence of native tin is that at the headwaters 

 of several rivers in New South Wales. About a year ago Dr. Samuel B. 

 Howell presented me with a specimen, and afterwards sent with another 

 the following letter, giving fuller information about its occurrence : 



"The washings I gave you sometime back came from Aberfoil river, 

 "about fifteen miles from the town of Oban, N. S. Wales. There is with- 

 " in two or three miles a very valuable diamond field, where corundum 

 " gems are common. The specimens I now send you are from the Sam 

 " river, which runs through the above-mentioned diamond field, twenty 

 " miles from the other locality. These rivers are the headwaters of the 

 "Clarence river, which empties into the South Pacific ocean. From this 

 "locality I have detected platinum, iridosmine, tin and gold ; the mineral 

 "formation appears to be the same." 



Both specimens showed the same association of minerals. 



