Royal Institution. 59 



the notch near anterior extremity very wide, and its anterior margin 

 blunt and projecting in form of a beak straight upwards ; posterior 

 extremity obtusely rounded, and terminating near the ventral margin 

 in a short blunt point. Dorsal and ventral margins nearly straight 

 or slightly arched. The surface of the valves is of a dull white colour, 

 and is densely and rather coarsely covered with impressed punctations. 



The carapace is convex, but much less so than in C, M'Andreit and 

 is of a much more oval shape. 



Hab. Near the Isle of Skye ; collected by R. M* Andrew, Esq., 

 August 1850. 



3. Cypridina Marine, Baird. 



Carapace valves elongate oval, of exactly the same size at each ex- 

 tremity ; extremities rounded. Dorsal and ventral margins nearly 

 plane, or very slightly arched. Surface of valves of a white shining 

 colour, mottled with a few spots of a dull white, and covered with 

 minute superficial punctations. Notch or ventral margin of anterior 

 extremity blunt, leaving the upper and lower margins of the notch 

 very obtuse. 



Approaches Asterope elliptica of Philippi somewhat in figure of 

 carapace, but is much more elongate, and is one-third larger. 



Hab. Off the Isle of Skye ; collected by R. M^Andrew, Esq., Au- 

 gust 1850. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



Friday, May 7, 1852.— W. R. Grove, Esq., M.A., F.R.S., 

 Vice-President, in the Chair. 



On the Supposed Analogy between the Life of an Individual and the 

 Duration of a Species. By Prof. Edward Forbes, F.R.S. 



In Natural History and Geology, a clear understanding of the rela- 

 tions of Individual, Species, and Genus to Geological Time and 

 Geographical Space is of essential importance. Much, however, of 

 what is generally received concerning these relations will scarcely 

 bear close investigation. Among questionable, though popular notions 

 upon this subject, the Lecturer would place the belief that the term 

 of duration of a species is comparable and of the same kind with that 

 of the life of an individual. 



The successive phases in the complete existence of an individual 

 are. Birth, Youth, Maturity, Decline, and Decay terminating in Death. 

 Whether we regard an individual as a single self-existing organism 

 however produced, or extend it to the series of organisms, combined 

 or independent, all being products of a single ovum, its term of 

 duration can be abbreviated, but not prolonged indefinitely, nor can 

 the several phases of its existence be repeated. Conditions may 

 arrest or hasten maturity, or prematurely destroy, but cannot, how- 

 ever favourable, reproduce a second maturity after decline has com- 

 menced. 



Now, it is believed by many that a species (using the term in the 

 sense of an assemblage of individuals presenting certain constant 



