NAVICULA INTERRUPTA. 47 
variation in size and outline; in some specimens an 0d- 
securely granular appearance of the strie can be observed, 
or rather the striz present the appearance of being tipped 
with granules, while in others they appear costate. Fur- 
ther, I have in certain portions of the valve, especially in 
very large specimens from the Red Sea, seen a granular 
appearance, not observable in other portions. After a 
most careful examination and comparison of numerous 
specimens from various localities, including those of 
Pinnularia pandura, Bréb., var. 8. elongata, of Prof. Gre- 
gory, sent to me by him from the Estuary of the Clyde, I 
feel convinced that the latter form is the typical N. Crabro 
of Ehrenberg. 
The form which Dr. Greville has figured as N. Crabro 
(Quart. Micr. Journ. vol. v. p. 7, pl. ui. fig. 11), from the 
West Indies, is, as I have ascertained from authentic 
specimens, and as believed by Mr. Ralfs, a different and 
distinct species, for which I suggest the name of N. Gre- 
villei ; it is smaller than N. Craéro, and distinguished by its 
compactly granular strie, which radiate from the centre of 
each lobe, and are much more conspicuous near the margin. 
Navicula interrupta, Kiitzing. 
Navicula interrupta, Kiitz. Bac. p. 100, t. xxix. fig. 93; Ralfs, in Prit. 
Inf. p. 894. 
Novicula ——, Bailey, in Amer. Journ. of Science, 1842, pl. il. fig. 18. 
Plate VII. fig. 2. 
V. divided into two oval or suborbicular lobes by a deep 
sinuous constriction; strie costate and radiating 
from the middle of each lobe, outer section coarse and 
conspicuous ; inner narrow, linear, faint ; intersecting 
groove straight ; median line broad. 
This species is readily distinguished from N. Apis, which 
