NAVICULA SUBORBICULARIS. 9 
striz divided by two longitudinal nearly parallel lines 
into three nearly equal sections ; the two outer costate 
and slightly inclined, the innermost faint and granu- 
lar ; median line broad. 
Mr. Ralfs (Prit.Infus. p. 899) has doubtfully referred 
this species to Pinnularia quadrifasciata, Ehren. (Mikrogeo. 
t. xix. fig. 27), so also has Rabenhorst without qualifica- 
tion (Europ. Diat.-p. 214). The two species, however, are 
very dissimilar in their specific characters ; Pin. (Navicula) 
quadrifasciata belongs to group B of the present sub- 
section, and is closely allied to N. spectadilis, Greg., 
differing chiefly in being narrower, and in the narrower 
sublunate form of the longitudinal unstriated area on each 
half of the valve. Ehrenberg gives two figures of Pin. 
quadrifasciata ; but one of them (fig. 25) is undoubtedly N. 
fusca, Greg. Both forms were discovered by him in the 
clay marl of Agina, associated with N. pretexta. All three 
occur together in the Red Sea, from which I possess speci- 
mens. WN. quadrifasciata has not been found in Britain, 
nor, to my knowledge, in the north of Europe. — 
Hab. Marine. In the ripples of the sandy beach be- 
tween tide-marks (abundant), on the coast of Northumber- 
land; New Brighton sands (Mr. Comber). 
Navicula suborbicularis, Gregory. 
Navicula Smithii, var. suborbicularis, Greg. Diat. of the Clyde, p. 15, 
pli. fig. 17. 
Navicula suborbicularis, Ralfs, in Prit. Inf. p. 898. 
Navicula forcipata, Grev., Rabenh. Europ. Diat. p. 178. 
Pinnularia forficula, O'Meara, Quart. Micr. Journ. n.s. vol. vii. p. 117, 
pl. v. fig. 9. 
Plate I. fig. 9. 
Frustule small. V. short, broadly oval or suborbicular ; 
median line broad, bordered by a doubly incurved 
