76 PROCEEDINGS OF THE ACADEMY OF 



the animal with a number of delicate filamentous pseudopods pro- 

 jected from the processes of the disk. The pseudopods as seen, 

 and as represented by Sandahl, are like those of the Foraminifera. 

 In the single-chambered character and structure of the case, 

 Astrorhiza resembles the fresh-water DifHugia, but differs in 

 having many orifices, to protrude the pseudopods, instead of a 

 single one. 



Notes on the Character of the Lower Silurian Slate at their Out- 

 crops. Prof. Frazer remarked that afine-graiued hydromica slate 

 from a point on the Peach Bottom Railroad, about five miles from 

 York, had been submitted to Dr. Genth for an investigation of the 

 amount of its alkaline constituents. 



The specimen was of greenish-gray color and semi-unctuous 

 lustre, and contained, in a chloritic mass, fine scales of mica, and 

 exceedingly fine particles of a mineral of apparently metallic 

 lustre. 



The water gave 2.36 per cent. 



Potash " 1.05 



Soda " 0.75 " 



With a decided trace of lithia (possibly from contained Lepido- 

 lite). 



Dr. Genth adds, "Taking the potash as belonging to Damourite, 

 we should have nearly 9 per cent, of it ; and the soda to parago- 

 nite there would be 9.6 per cent." 



The mass of this rock is chloritic while the small speck of pearly 

 mica-like mineral might be Euphyllite, or (in view of the per cent, 

 of Li) Cookeite. In the former case both the K and Na would 

 be associated together in the same constituent, while the Li would 

 remain unaccounted for. Vogtite, Margarodite, or the species 

 examined by Smith & Brush, from Litchfield, Connecticut, and 

 which was intermediate between Margarodite and Paragonite, 

 might be represented. 



But the plan proposed by J. D. Dana, of characterizing these 

 partially decomposed slates simply as h}^dro-mica slates, seems to 

 fulfil every requisite of accuracy. 



March 23. 

 The President, Dr. Ruschenberger, in the chair. 

 Twenty-nine members present. 

 The following papers were presented for publication : 



" On Buteonine Subgenus Craxirex, Gould." By Robert Ridg- 

 way. 



"On Nisus Cooperi, Bonaparte, and N. Gundlachi, Lawrence." 

 By Robert Ridgway. 



