H. S. 'Williams — Ventral Plates of the Holonema. 285 



In many stony meteorites olivine is a considerable constituent, 

 generally forming the bulk of the soluble silicate ; but in this 

 case the analysis shows olivine to be present in but small pro- 

 portion, if at all. It is interesting to note that both the soluble 

 and insoluble portions have practically the same molecular 

 ratios, the soluble portion reducing itself essentially to 

 RAl 2 SiO e , in which R=Ca, Fe; and the insoluble part to the 

 same formula, where R=Mg, Fe ; both being equivalent to 

 aluminous enstatite or pyroxene. 



At the time this analysis was made it was impracticable to 

 supplement the work with the proper microscopical examina- 

 tion of sections, which, doubtless, in conjunction with the 

 chemical evidence would have satisfactorily determined the 

 minerals present. Without this microscopical knowledge, how- 

 ever, little that is definite can be said, except that there seem 

 to be present two similar molecules ; the one in which lime 

 predominates being soluble, and the other, magnesian, being 

 insoluble in hydrochloric acid. 



The other alternative is to assume a complex molecule which 

 is split into two sections by the action of the acid. 



The meteorite is now known as the Safford meteorite. 



Laboratory TJ. S. Geological Survey. 



Art. XLIII. — On the Ventral Plates of the Carapace of the 

 genus Holonema of Newberry ; by Henry S. Williams. 



In the summer of 1890 I exhibited photographs of several 

 plates, associated together on a slab of sandstone which I 

 referred to Holonema, one of the plates (m. v. of figure 

 beyond) being the same in shape and markings as the orig- 

 inal plate described by Claypole as the " ventro-median " or 

 "lozenge-plate" of "Pterichthys," and named by him Pter- 

 ichthys rugosa* Messrs. Cope and Claypole both examined 

 my photograph at the time and remarked upon the close 

 resemblance to the arrangement of plates on the back of 

 Bothriolejpis. In the account given by Claypole in the 

 American geologist, f the plates are described as dorsal, and 

 their position is reversed, the plate a. m. v., or anterior median 

 ventral, being called " post-dorso-median," although the general 

 shape of the plates is correct, it having been reproduced, 

 mainly, from a copy of my photograph.^ 



In the Proceedings of the U. S. National Museum, vol. xiv, 

 p. 256, Cope refers to the same photographs as representing 



* Am. Phil. Soc., 1883. f Vol. vi, p. 255, 1890. 



% See figure, ibid., page 256. 



