MacMillan: OBSERVATIONS ON PTERYGOPHORA. 729 
cidedly flattened, measuring 9 mm. in width by 3 mm. in thick- 
ness. The pinne do not stand always directly opposite each 
other, although this in general is their position. Abortion of 
one pinna of the pair may be observed in this plant at two points. 
The base of the pinne is more attenuate than that of the cen- 
tral lamina. The holdfast is partly cut away, but is flattened 
out and compacted much more than in plant B. 
Plant «*D.” This plant was collected in July, preserved in 
formalose, and brought to Minneapolis for study. It was found 
growing with several others about twelve feet below the surface 
of the water at low tide. The stipe from the holdfast to the 
lowest pinne is 2 meters in length. From the lower pinne to 
the base of the central lamina is 1 dm. while the central lamina 
is I.5 meters in length. On each side of the stipe, extending 
along its margin for a little less than a decimeter, are the tufts 
of lateral pinne, twenty on each side. The longest pinna with 
uneroded end measures I meter, but pinne with eroded ends 
are present, 1.5 meters in length. The breadth of the central 
lamina is 1 dm., the midrib being 4 cm. broad. The broadest 
pinna measures 7.5 cm. from margin to margin. All margins 
of full grown pinne are undulate. This character is especially 
marked in the central lamina. One difference between a plant 
of the age of ‘‘D” and a younger form such as ‘*C” lies in 
the distance between the adjacent pairs of pinne. In plant 
«¢C,” for example, the upper pinne are three cm. apart along 
the stipe and this character is also indicated in Ruprecht’s 
plate. In an older plant, such as‘‘D,”the pinne are very 
much crowded together, so much so, indeed, that they crowd 
each other out of a strictly marginal position. The fully de- 
veloped pinnae, in ‘‘ D” are all massed within a linear distance 
of 5 cm., while in ‘* C” they are distributed over twice as much 
space. 
The stipe in this specimen is 5 cm. in diameter, 2 dm. above 
the holdfast. Near the holdfast itis 1 dm. in diameter. Nearer 
the pinnz it becomes flattened in cross section, first appearing 
as elliptical, then as lenticular, the edges becoming sharp 2 dm. 
below the lowest pinne. Along the sharp edges the scars of 
pinne which have been sloughed off are abundant. ‘The stipe 
in the region of pinna attachment is 3 cm. broad and 7.5 mm. 
thick. The stipes of the full-grown pinne are 4 mm. in diameter 
and the base of the central lamina is 1 cm. broad and 3 mm, in 
