12 M. F. Plateau on the Freshwater Crustacea of Belgium. 



of the pinna?, as it is not easy to separate them from the 

 leaves, and I have not yet seen an entire specimen. 



Mertensites crenata (nobis). PI. I. fig. 3. 

 Segments of the pinna? crenato-lobate and rather broader than 



those of M. hantoniensis. 



This species is much rarer than the preceding. I have a 

 specimen which indicates a pinna 4 inches broad. It seems 

 to be altogether on a larger scale than M. hantoniensis. 



Croziers and fragments of stipites belonging to one or other 

 of these species have been found ; the stipites would indicate a 

 fern probably 4 to 5 feet in length. 



I hope at some future time to obtain specimens which will 

 enable me to determine the rarer forms, figs. 4 a, b, and 5. 

 All that I can say of them is that fig. 4 seems to be allied to 

 Lindscea or Adiantum, and fig. 5 to some genus of Cgathece. 



EXPLANATION OF PLATE I. 



Fig. 1 a. Part of pinna of M. hantoniensis, showing the venation. 



1 b, c, d, e. Ultimate branches, showing the habit of growth. 



If, g. Fructification. (\g is enlarged.) 

 Fig. 2. Stipes of Mertensites (reduced, one-half). 

 Fig. 3. Part of pinna of M. crenata. 

 Figs. 4 a, b. Adiantum ? 

 Fig. 5. Cgathece ? 



IV. — Investigation of the Freshwater Crustacea of Belgium. 

 By FfiLix Plateau. (First Part.) * 



The study of the little freshwater Crustacea, already carried 

 so far by Miiller, Jurine, and Straus, was resumed in 1837 by 

 the English zoologist Baird, who extended the circle of our 

 knowledge with regard to them, and set himself to describe 

 the species (especially of the genus Cg^pris) which are met 

 with in England. 



I have made some investigations of the same kind in Bel- 

 gium, which, wedged in between France, Holland, and Ger- 

 many, has a fauna partaking of those of these three countries, 

 and consequently very rich. 



The present memoir, which is only the first part of my work, 

 contains the results of my anatomical and physiological obser- 

 vations upon the genera Gammarus, Lgnceus y and Cgpris^ as 

 also a list of the species of these genera which are met with in 

 Belgium. In this summary I shall leave this list unnoticed. 

 I may state, however, that the number of species which it con- 

 tains is distributed as follows : — three for the genus Gammarus, 



* For this abstract, as also for a copy of the original memoir, from 

 " Tome xxxiv. des M6moires couronnes publics par l'Academie de 

 Belgique," we are indebted to the author. — W. F. 



