OF AMERICAN SPIDER. 55 



The species which I am treating; of, is of ar black 

 colour, inclining to blue; the abdomen is marked 

 with about ten livid pale spots, and a line towards its 

 anterior extremity : 1 have seen specimens where the 

 legs \\ ere marked with black spots. I think it ne- 

 cessary to remark here, that spiders of the same spe- 

 cies living in dark, places, vary greatly in their co- 

 lours, according to the manner in which the light 

 strikes upon them. The great point in this case I 

 think, is to ascertain the genus, for it appears that the 

 web of all species belonging to it, has the same 

 virtues, and this is distinct from the Aranea Domes- 

 tica, whose web has been used in Europe : we see 

 an illustration of this in the genus meloe, where every 

 species possess more or less the blistering power. 



The present American spider, I think, has not 

 been as yet described : for the present I shall call it 

 Tegeneria Medicinalis. — PI. V. fig. 1. 



a — organs of manducation. 



b — position of the eyes. 



Description of some new crystalline forms of tlie 

 minerals of the United States. By Dr. G . Troost. 

 —Read March 6, 1821. 



As yet but little attention has been paid to the 

 crystalline forms of the minerals of this country, 

 many of which have no analogies with those described 

 by European crystallographers. Among this num- 

 ber may be mentioned a variety of phosphate of lime, 

 with the description of which, I have now the honor 

 to present the Academy, and hope to continue the 



