Fisher — Elevation of Mountain Chains, 493 



would have been rather more elevated above the body ; but they 

 never could have occupied the same erect position which they do in 

 A. Kowfilewslcii. 



In glancing at the structure of the eyes in Insects we find only 

 two genera with pedunculated eyes in the whole Class. These occur 

 among the Diptera; Diopsis subf aetata, and Acliias oculatiis, having 

 their eyes placed upon the extremities of long-fixed eye-stalks.* 



Further investigation will no doubt afford additional information 

 on this interesting discovery, meanwhile I have thought it so impor- 

 tant that I have at once recorded it, that those best able may add 

 fresh evidence in correction or corroboration thereof. 



EXPLANATION OF PLATE XXI. 



Fig. L Calymene ceratophthalma, sp. nov. Wenlock Limestone, Dudley. Figured of 

 the natural size. (The cheeks and tail slightly restored.) From the col- 

 lection of Mr. E. Hollier, Dudley. 



„ 2. Calymene Blumenbachii, Brong. Wenlock Shale, Dudley. Coiled-up speci- 

 men ; natural size. Figured to show the usual condition of the eyes (o), 



„ 3, Asaphus expansus (natural size) from the Lower Silurian, Pulkowa, Russia. 

 Side-view of a coiled-up specimen preserved in the British Museum. 



„ 4. AsapJms Koivalewskii, (natural size). Lower Silurian, Pulkowa, near St. 

 Petersburg (front- view of a coiled-up specimen ; natural size). 



,, 5. Asaphus KowalcwsJcii, (side-view of same ; natural size). 



,, 6. Encrinurus variolaris, side-view of a specimen from Dudley, in the British 

 Museum, showing the somewhat prominent form of the eyes. (Nat. size.) 



„ 6a. One of the eyes of the same enlarged to show the position of the suture ana 

 the cornea of the eye. 



„ 7. Ceratoccphalus Grayianus ("White, MS.) (enlarged three times) from Flinder's 

 Island, Bass' Straits. Coll. Brit. Mus. 

 Showing the sessile eyes (o, o) and the pseudo-eye-stalks [p, p). 



„ 8. Eye-peduncle of Gelasimus platydactylus, shomng the prolongation of 

 peduncle beyond the cornea of the eye. 



,, 9. Eye-peduncle of Gonoplax angulata, showing eye at the extremity of same. 



„ 10. Eye-peduncle of Ocypoda ceratophthalma, showing prolongation of peduncle 

 beyond the cornea of the eye. 



II. — On the Elevation of Mountain Chains,^ with a Speculation 

 ON THE Cause of Volcanic Action. 



By Rev. 0. Fisher, M.A., F.G.S. 



IT is some months since I read a paper at the Cambridge Philo- 

 sophical Society, to which reference has been made in your 

 pages by Mr. Maw.' I do not think that I shall be out of order 

 in sending you a short outline of the substance of it. 



Mr. Maw's letter in the March number of the Magazine * led me 

 to calculate what the horizontal pressure at any point of a thin, outer 

 spherical shell of the earth might be, and the result I obtained was 

 that which Mr. Maw has already communicated to you from a 

 private letter of mine. If you take into consideration a spherical 

 shell of a few miles thickness, and conceive it for a moment unsup- 

 ported by the matter within, then the horizontal pressure upon each 



^ Among the Arachnida there is a little spider in the genus WalcJcencera {W' 

 acuminata), the male of which has a tall and slender central fixed peduncle, upon 

 which the eyes are placed, two at the summit and foui* midway on either side. 

 2 See also Mr. Shaier's Article at p. 511. 3 Vol. V. p. 294. * Vol. V. p. 149. 



