Mr. Brooke on Mengite, and other Minerals. 187 



expert in climbing, nor so tenacious of life under similar cir- 

 cumstances. I may remark, that in experiments instituted to 

 decide how long spiders can live without food, the influence 

 of season should not be disregarded. In winter, unless a high 

 temperature be maintained by artificial means, the vital func- 

 tions are performed with much less energy than they are in 

 summer : of course the natural demand for sustenance, if it do 

 not cease altogether, is gi'eatly diminished in the former period, 

 and the animals suffer little comparatively from abstinence. 



Another spider of a diminutive size, frequently observed to 

 take aerial excursions, is the Drassus ater of Latreille, which 

 appears to be identical with Xho-Aranea o6^^ci^r2.r of Bechstein. 



Aeronautic spiders, properly so called, or those species 

 which instinctively en)p]oy their lines to sail in the atmosphere, 

 will probably be found almost exclusively among such as are 

 active during the day and decidedly eri'atic. Numerous facts 

 tend to corroborate this idea, the correctness or inaccuracy 

 of which can only be determined by more extended observa- 

 tions. 



XXIV. On Mengite, a new Species of Mineral; on the Cha- 

 racters of' Ae^ichemie ; o« Sarcolite, as distinct Jrmn Anal- 

 cime a?id Gmelinite ; with other Mineralogical Notices. By 

 H. J. Brooke, Esq. F.R.S. L.S. ^' G.S. 



A 



Ilmenite. 



MINERAL under this name is said to have been de- 

 scribed in 1821 in Kastner's Archiv., &c. No. 1. by Prof. 

 Kupffer of Kasan. It was discovered by Mr. Menge, near 

 Lake Ilmen in Siberia, accompanied occasionally by a tita- 

 nious iron-ore in modified rhomboids, of which a description 

 and figure, but without measurements, were given by Mr. Levy 

 in the Phil. Mag. and Annals, N.S. vol. i. p. 26. 



Probably from having seen only the iron-ore, Prof. Rose 

 of Berlin has stated that this was the ilmenite of Kupffer. 

 The ilmenite is, however, a distinct substance, having for its 

 primary form u right rhombic prism of 136° 30', the terminal 

 edge being to the lateral edge very nearly as 17 to 1 1. The 

 colour is a more intense black than the rhomboids of titanious 

 iron, and the surfaces of some of the crystals are perfect and 

 brilliant. I have not observed any cleavage; the fracture is 

 uneven to conchoidal with a vitreous lustre. Spec. grav. S'iS. 

 Scratches glass slightly. The matrix is clcuvelandite. 



The crystals I have examined are generally small, length-. 

 2 B 2 ened 



