NAVICULA CRUCIFORMIS. 65 
I have been induced to reduce N. pectinalis, Bréb., of 
Smith’s Synop. to a synonym of N. retusa, Bréb., because 
the valve of the latter corresponds with Smith’s description 
of that of the former, which does not accord with any other 
allied species, and because of the following observation of 
Prof. Walker Arnott on the subject :—“It is not to me quite 
clear on what De Brébisson originally bestowed the name 
of N. pectinalis; what Smith received from him and sup- 
posed to be so, I have reason to think was N. retusa, of 
which Smith only knew the F. V.; and in that state it is 
almost undistinguishable from N. pectinalis of the Synopsis” 
(Quart. Micr. Journ. vol. vii. p. 176). 
Hab. Marine: frequent in sand-gatherings near estua- 
ries. 
+ More or less inflated in the middle. 
Navicula cruciformis, Donkin. 
Navicula cruciformis, Donk. Quart. Micr. Journ. n. 8. vol. i. p. 10, pl. i. 
fig. 7. 
Pinnularia Brébissonit, var. d, Rabenh. Europ. Diat. p. 222, 
Plate X. fig. 4. 
Frustule on M. V. broad, oblong, quadrangular, constricted 
in the middle, angles bevelled. V. linear, slightly 
inflated in the middle, extremities rounded; striz 
reaching to the median line, very oblique, and diver- 
ging midway between the central and terminal nodules, 
costate, 30 in -00L", absent (so as to leave a broad 
cuneiform blank space) opposite the central nodule ; 
dry valve brown-coloured. 
Rabenhorst has referred this species to N. Brébissonii as 
a variety, forgetting that I described it as being a marine 
