02 



SCIENCE-GOSSIP. 



[March 1, 1S66. 



pinnated leaves, whose leaflets are auriculate at 

 the base." In addition thereto we may mention 

 Coniopteris, Pachypteris, and Phlebopteris, three other 



Fig. 75. Olopteris cune xta. 



genera of Eerns not illustrated in this or the pre- 

 ceding notice; and Pecopteris, the figure of one 

 species of which will be found at page 37. The 

 species found in the Lower Oolite is Pecopteris 



Desnoyersii. 



BRITISH DIATOMS. 



YIELDING to the recruest of some of our sub- 

 scribers we have made arrangements to 

 supply, from time to time, illustrations of the genera 

 of British Diatoms. More than this we can scarcely 

 promise at present, because we do not wish that 

 Diatoms should become an important feature to the 

 exclusion of other topics, and the aunoyance of 





Fig. 76. Navicula didi/ma. Fig. 77. Pinnuhiria major. 



those who do not care, or do not need, to be 

 troubled with them ; and because the subject is an 

 expensive one, as well as a difficult one, to illustrate 

 satisfactorily. 



There is already a handy-book in existence which 

 will supply what is necessary in classification and 

 furnish the names of the species. This is Dr. Gray's 

 " Handbook* of British Algse, with the Diato- 

 maceee," by Mr. W. Carruthers. Hence there 

 , will be less necessity for us to adhere to a 

 strict systematic order in publication, because 

 I it will be easy to refer the genera illustrated to 

 their place in the system adopted in the hand- 

 book. 



The species now figured, if not really typical, 

 will serve to illustrate four genera of the group 

 called Naoiculece. The characters of this group 

 are described as " valve with similar ends, and a 

 median longitudinal line ; front view, linear or quad- 

 rangular; frustules free, concatenate, or included in 

 a gelatinous frond." 



Navicula is a very large genus, containing not 

 less than eighty-four British species. The valve is 

 furnished with delicate moniliform stria, and has 

 central and terminal nodules (fig. 76). 



Pinnularia is also an extensive genus, including 

 fifty-three British species. The valve has distinct 

 ribs, or costse, with central and terminal nodules 



(fig- 77). 



Stauroneis is a much smaller genus, of which 

 we have but sixteen British representatives. The 

 valve in this genus is striated, and the central 





la 



Fig. 78. 

 Stauroneis Phaeiucenteron. 



Fig. 79- 

 Pleurosigma formosum . 



nodule is transversely dilated into a band, which is 

 free from stria; (fig. 78). 



