GrevillEj on New Diatoms. 
17 
third longer than the indmdual figured. Those kindly com- 
municated by my friend^ Dr. Abercrombie^ of Cheltenham, 
from Berbice, are generally small, and occur along with fine 
varieties of N. permagna of Bailey, which I hope to illustrate 
in a future paper. In the same gathering is also a long 
Pleurosigma, apparently intermediate between P. Balticum 
and P. longinum. (Brightwell, ^Mic. Journ./vol. vii, p. 180, 
plate ix, fig. 7.) 
Navicula Johnsoniana, n. sp., Grev. — Valve somewhat con- 
vex, elliptical-oblong, with slightly produced, obtuse extremi- 
ties, and a transversely rounded, stauros-like blank space in 
the centre ; striae very oblique, conspicuously lineato-punctate. 
Length -0034" to -0040". (Fig. 8.) 
Hab. New Zealand ; C. Johnson, Esq. Harvey Bay, 
Queensland, in a dredging communicated by Dr. Roberts. 
Again I have the pleasure of recording one of the many 
discoveries of my esteemed and venerable friend, Mr. John- 
son, of Lancaster. It is only recently that he detected the 
present diatom in his New Zealand slides, and kindly pre- 
sented me with one containing several specimens. I had, 
however, scarcely prepared my description before I recog- 
nised the same thing in an Australian dredging transmitted 
by Dr. Roberts, in which it appears to be exceedingly rare. 
It is a somewhat remarkable species, being intermediate be- 
tween the genera Navicula and Stauroneis, and I have been 
mainly induced to place it in the former, on account of the 
nodule being sufl&ciently definite apart from the rounded 
blank space into which it expands on each side, and because 
this blank space is unequal, being always larger on one side 
than the other, as in many Pinnularice, The most striking 
feature in the valve is the conspicuous, remote, oblong 
puncta, and the very oblique striae into which they are dis- 
posed. The median line is prominent, and there is a 
straight parallel row of puncta on each side. A difference 
exists between the New Zealand and the Australian examples. 
In the former the frustules are oblong, the puncta larger, 
and the striae 16 in '001." In the latter the frustules are 
elliptical-oblong, the puncta much smaller, and the striae 22 
in '001". This is certainly a considerable discrepancy, but 
the recent study of these wonderful little vegetables has led 
to the conclusion that far too much importance was formerly 
attached to number in the markings, and that it would be 
desirable to establish characters, if possible, upon other 
grounds. I had prepared drawings of both forms j but not 
having room in the plate for both, I have given the Austra- 
lian, on account of the more highly developed central-nodular 
VOL. II. b 
