252 Dr. Greville on some British Diatomacese. 



June 29th, one east skin was removed. 

 July 4 th, one „ „ 



„ 9th, one „ „ 



„ 11th, one „ „ 



At this date four individuals were given to a friend, so that 

 the number was reduced to four. 



July 1 5th, one cast skin was removed. 



„ 17th, one „ „ 



„ 18th, one „ „ 



„ 21st, one „ „ 



„ 30th, one „ „ 



August 3rd, one „ „ 



„ 4th, two „ ,, 



„ 12th, one of the prawns died during the moulting. 

 „ 14th, one cast skin was removed from the aquarium. 

 „ 21st, one „ „ „ 



September 2nd, one „ „ „ 



So that the period appears to vary from twelve to twenty-four 

 days. This variation may depend upon the quantity of food 

 taken by the respective individuals, and also on the varying 

 temperature of the aquarium, which, from its small capacity and 

 other circumstances, is very liable to be readily affected by the 

 heat of the sun through the day, and the effects of radiation 

 during a clear night. I may mention that if these cast skins 

 are not removed from the water, the prawns will devour all the 

 smaller and softer parts, as the legs, the palpi, and the false or 

 swimming feet, with great rapidity. 



I hope in a future communication to add several observations 

 on other varieties of the PalcemonidcB. » 



Apothecaries' Hall, Blackfriars, March 12, 1855. 



XXIII. — Report on a Collection of Diatomacese made in the 

 District of Braemar by Professor Balfour and Mr. George 

 Lawson. By R. K. Greville, LL.D. &c.* 



[With a Plate.] 



In the course of the autumn of last year. Professor Balfour made 

 a botanical excursion with a small party of friends and pupils to 

 the mountainous district of Braemar ; and his attention having 

 been directed for some time past to the Diatomacese, he, and 

 Mr. George Lawson made a considerable number of gatherings 

 in a great variety of situations, from the patches of snow which 

 even in summer are always to be found in certain nooks and 



* Read before the Botanical Society of Edinburgh, Feb. 8, 1855. 



