THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 87. MARCH 1865. 



XVIII. — Conjugations of Navicula serians, N. rhomboides, and 

 Pinnularia gibba. By H. J. Carter, F.R.S. &c. 



[Plate IV.] 



It is now just nine years ago (viz. in January 1856) that my 

 descriptions of three species of Diatomese in conjugation re- 

 spectively were published in the ' Annals' ; and since that time 

 so little has been done in the subject that hardly more than a 

 dozen instances appear to have been added ; at least the late and 

 lamented Prof. Smith, in his ' Synopsis ' (I quote from the ex- 

 cellent article on the Diatomeae in Pritchard's last edition of his 

 ^ Infusoria ' for all references of this kind), enumerates but thirty- 

 two species ; and twenty had been observed (my own included) 

 when I made the communication from Bombay in the * Annals ' 

 to which I have alluded; while among all these conjugations 

 there appears only one instance in a Navicular form, viz. that 

 found by Dr. Griffith in 1855, and published by him in the 

 ' Annals ' a few months before my own paper. This presented 

 such a remarkable feature in addition to what had already been 

 shown, viz. the presence of a transversely ringed siliceous sheath 

 enclosing the sporangial frustule, that it has ever since been 

 desirable to determine if instances of it in other Navicular forms 

 might indicate its usual occurrence among them also, or its ex- 

 tension to the conjugation of the Diatomese more generally. 



Anxious to satisfy myself on this point, I have often, since 

 the publication of Dr. Griffith's interesting discovery, sought for 

 a conjugation of the kind ; and although I have frequently met 

 with isolated instances of conjugation in Gomphonemaj Cyclo- 

 tella, and Melosira in Bombay, as well as latterly in Devonshire, 

 it was not until the beginning of the month of July last (1864) 

 that I happened to fall in with a number of Diatomese among 



Ann, S^ Mag, NaL Hist, Ser.3. Fo/.xv. 11 



