" 42 FIELD CoLUMBIAN MusEuM—GEo Locy, Vot. III. 
. 
nodules are of a light cream color, with membranous patches of 
red and brown dried organic matter, (Meloboes1a) which continues to 
produce the characteristic pungent odor of drying marine vegetation. 
From the weights and dimensions of 56 individuals, the writer has cal- 
culated the average size and shape. Itisarounded body, like a slightly 
crushed sphere, 9.9 centimeters long, 8.7 centimeters wide, and 7.6 
centimeters thick.. Its weight is 340 grams. The variation of size 
in the nodules at hand is considerable, the maximum diameters of 
the 56 individuals lying between 6.8 and 14 centimeters, and the 
minimum diameters between 5.7 and 11.2 centimeters. The corres- 
ponding weights are 118 and 940 grams. Between these limits the 
sizes and weights of the nodules are distributed with a fair degree of 
uniformity. While the individual nodules frequently depart far 
from a true spherical form, they appear on casual inspection to do 
so in all possible directions, and with no tendency toward any other 
definite shape than the sphere. When the dimensions of all the 
specimens are tabulated, however, it appears at once that the 
majority of the forms are such that the three perpendicular axes or 
diameters are unequal, and the length of the intermediate is an 
arithmetical mean between the longest and the shortest diameter. 
The average nodule, as described above, also has this form. Few of 
the specimens depart far from these proportions. Many, however, 
while maintaining their ratios between major, median, and minor axes 
do depart materially from the form of the spheroid of the same axes. 
One is in the form of a cone with a large, shallow depression in its 
base, Well to one side of its axis. (Plate XXVI, Fig. 6.) Others have 
slight flattenings and concavities which are suggestive. Frequently, 
on the flatter sides of the nodule there will be slight depressions a 
little to one side of the centre. These forms dimly but persistently 
suggest half-obliterated forms of familiar gastropod shells. (Plate 
XXVI,) | | 
The specific gravity, of a specimen weighing 540 grams was 
found to be 2.30.* | 
The surface of the nodule (Plate X XV) is always of an irregularly 
rough or warty appearance. It is composed entirely of the skeletons 
of calcareous encrusting organisms which are chiefly corals, bryozoa 
and algae. In places the surface is covered with cylindrical branch- 
ing forms, (Madracts ?) which may attain a height of 8 mm. and a dia- | 
meter for individual cylinders of perhaps 2mm. ‘These forms were 
all dead when the specimens were collected, and are in all instances 
* See p. 50 for cause of low results. 
