1887.] NATURAL SCIENCES OF PHILADELPHIA. 311 



known. This mineral occurs in pale grayish yellow, stellate masses, 

 somewhat resembling karpholite or pyrophyllite. It is associated 

 with calcite. The stellate aggregation is readily friable as it breaks 

 into minute prismatic particles. Made into an artificial splinter, the 

 substance fuses in the oxydizing flame to a black glass. Heated in 

 a closed tube it yields abundant water at a red heat, changing its 

 color to chocolate brown. The water does not act acid, nor corrode 

 glass. Carefully dissolved in a borax bead, the latter remains color- 

 less at first, then gradually assumes the characteristic manganese 

 color. The powder dissolves in hot concentrated hydrochloric acid 

 but does not gelatinize. The specific gravity (determined with 

 1.4230 gram.) is 2.981. 

 The analysis gave 



SiO' =39-00 

 MnO = 42-12 



100-00 



The determination of iron was lost, its quantity is made up by the 

 difference. Manganese is present as MnO ; (the peculiar behavior 

 in borax mentioned above, and the absence of any evolution of chlo- 

 rine, when dissolved in HCl are proofs of this assertion.) Calcium 

 is only present in traces and was Aveighed with the magnesia. 



If we calculate the molecular ratio of the oxyds we obtain 

 (MnO, WO, FeO, ZnO, MgO) : SiO^ = 1 : 231 : 0-65 = 1-89 

 : 1 = 2 : 1. 



This is the ratio of an orthosilicate, and in fact is the molecule 

 of Tephroite, in which a considerable portion of manganese is re- 

 placed by water. That the water must be considei-ed as basic, fol- 

 lows from the fact that none is expelled at 200 C. The low spe- 

 cific gravity is very extraordinary and seems to indicate a polymeric 

 condition of the molecule. The name Bementite is proposed for 

 this species. 



Remarks on Hydra : Prof. Leidy remarked that in our fresh 

 waters there occur two well marked species of hydra, the one of a 

 bright green color, the other pale brownish or reddish. He contin- 

 ued, these, jud'gingfrom descriptions and figures, appear to him to be 

 the same as the Eurojiean species H. viridis and H. fusca. The late 

 Prof L. Agassiz regarded them as different and named them H. 

 gracilis and H. eartiea (Proc. Bos. Soc. Nat. Hist. 1850, 354.) 

 Familiar as he was with both the European and American animals 

 his opinion might be considered conclusive, but the only distinctive 

 character he assigns to each seems not to be correct. Of our green 

 hydra he observes that unlike the European it has the power of ex- 

 tending its body in a remarkable degree. Opposed to this view, 



