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narrowness, when compared with the cones of the genus Pinus .This is the other circumstance to which I alluded ; but this form, itis to be remarked, is in perfect agreement with the proportions ofthe supposed fossil strobilus at PI. IX. Fig. 1, and is to be con-sidered as strengthening the opinion, that many genera, as well asspecies, of vegetables, have existed, and been destroyed ; and ofwhich we have no other traces than their remains in a fossil state.For some very excellent observations on this curious fossil, I mustrefer you to that elegant work, Petrijicata Derbiensia.

The fossil at PL X. Fig. 1, also serves, in my opinion, to explainthe nature of the fossil depicted at PI. III. Fig. 6, and alreadyspoken of in a former Letter; since, if the conjectures just offeredbe right, this fossil, which has so much puzzled oryctologists, maywith the greatest reason be supposed to be the Amentum, or Catkin,from which that kind of strobilus, the existence of which has beenjust inferred, has been formed. The specimen depicted at PL IX.Fig. 10, serves also to render more probable, that the flattenedspecimens already described, .and figured at PL I. Fig. 6 and 7?and Pl. V. Fig. 8, are the remains of plants of the succulent tribe.Every appearance which this specimen presents, serves to show thatit very nearly resembles the Cactus Cochenilifer, one of those plantsgenerally known by the name of Indian figs; and on which thatcurious insect, the Cochineal (Coccus Cacti) feeds and inhabits.

Yours, &c.