Botanical Society of Edinburgh. 311 



Prof. Forbes proceeded to observe, that such animals as are com- 

 mon to many zones of depth are those which have the greatest hori- 

 zontal range in space, and are generally those which are present in 

 the tertiary deposits ; and thus it is that the most generally- distributed 

 fossils are such as are found in the greatest number of formations ; 

 because these are necessarily the most independent of destroying in- 

 fluences. But, on the other hand, as the elevation or depression of 

 strata to a very small extent would destroy the species peculiar to 

 any zone, or to the zone above or beneath it, it becomes an import- 

 ant inquiry how this destruction is compensated. In dealing with 

 this question, Prof. Forbes announced a most important law in zoo- 

 logy, one altogether new to ourselves — viz. That the mollusca migrate. 

 He discovered by his own observation, that this is the case even with 

 the limpets, the most fixed of all species. This migration occurs in 

 their egg-state, when the ova are strung together and floated over 

 the ocean, from shore to shore. In the larva state they are swim- 

 mers. In fact, they commence their life in a form closely analogous 

 to that which is permanent among the Pteropods ; but though in 

 this state they can live in any zone, they cannot arrive at perfection 

 except in the peculiar zone to which they are adapted. This accounts 

 for the very imperfect shells of prematurely-dying mollusca being 

 found at a low depth. Professor Forbes concluded his communica- 

 tion by noticing its bearings on the views of the most eminent geo- 

 logists of our time. 1st. With regard to Mr. Lyell's principle of 

 distinguishing tertiary strata by the per-centage of recent species in 

 each. This is confirmed by Prof. Forbes's investigations ; only in 

 using Mr. Lyell's criterion, the element of depth, which gives cli- 

 matal character in living animals, must be taken into account. 2nd. 

 Prof. Forbes next noticed that Sir H. De la Beche had hypothetically 

 anticipated, what his researches established, the representations of 

 climates and depth, ten years ago. 3rd. He lastly ascribed to Vis- 

 count d'Archiac and M. de Verneuil the credit of having announced 

 (what he had observed and mentioned in the course of his commu- 

 nication), that species which are found in a great number of localities, 

 and in very distant countries, are always those which have lived ' 

 during the formation of several successive systems. — Athenceum. 



BOTANICAL SOCIETY OF EDINBURGH. 



This Society met on Thursday, the 8th of February, Professor 

 Graham in the Chair. 



The following communications were read : — 



1. Two papers " On the British Desmidiacea," by Mr. Ralfs. 



2. *• On some species o{ Cuscuta," by Mr. C. C. Babington, MA., 

 F.L.S. &c. (Inserted in the present Number.) 



3. " On the Marine Algse of the vicinity of Aberdeen," by George 

 Dickie, M.D., Lecturer on Botany in the University and King's Col- 

 lege of Aberdeen. 



All these will shortly appear in the ' Annals and Magazine of Na- 

 tural History.' 



