18 NAVICULE®. 
nular, convergent, and of unequal length around the 
centre, reaching to the median line near the extre- 
mities, then gradually receding from it towards the 
central nodule, around which they leave an orbicular 
blank space. 
Hab. Marine. Lamlash Bay Isle of Arran, Estuary of 
the Clyde, Glenshira sand (Prof. Gregory). This appears 
to be a deep-water species, not being found on the beach 
associated with N. humerosa. 
Navicula humerosa, De Brébisson. 
Navicula humerosa, Bréb. in Sm. Synop. vol. ii. p. 98; Ralfs, in Prit. 
Inf. p. 903; Rabenh. Europ. Diat. p. 201. 
Navicula quadrata, Greg. Trans. Micr. Soe. n. s. vol. iv. p. 41, pl. y. 
fig. 5. 
Navicula crassa, Greg. Quart. Micr. Journ. vol. iii. p. 41, pl. iv. fig. 18? 
Plate IIT. fig. 3. 
Frustule large. V. linear-elliptical, somewhat suddenly 
contracted into produced, broad, flattened apices ; 
strie very oblique, radiating around the centre, di- 
stinctly granular, about 25 in 001", reaching near to 
the median line, but shortened so as to leave a broad 
blank space opposite the central nodule. Dry valve 
colourless. 
This species is very variable in size and outline. In 
elongated specimens it is frequently constricted in the 
middle ; it is closely allied to N. latissima and N. granulata, 
but readily distinguished from it by its very much finer 
strie, and by its outline near the extremities, which are 
much more produced. 
Hab. Marine. Common on the sea-shore in the sandy 
ripples between tide-marks, and generally associated with 
N. granulata. 
