VAN NAME: COMPOUND ASCIDIANS. 
381 
spicules were from Canadian waters. Redikorzew (1908b, p. 52) 
mentions spicules of O.K) to 0.175 mm. diameter in European speci- 
mens, but these are probably to be understood as extreme dimensions. 
Certainly no such average is attained in American examples. 
The shape of the spicules is not properly described as stellate, but 
is that of a sphere studded with numerous short blunt projections 
which taper slightly and have almost hemispherically rounded ends. 
When the spicules are abundant their shape as well as their size and 
distribution are usually beautifully uniform, especially in the upper 
layers of the colony. Occasional specimens may be met with in which 
the spicules are much reduced in number and size, and in such cases 
they often exJiibit irregularities in shape also. Some colonies from 
Station 157 (off Cape Ann, 
Mass., N. lat. 45° 35', W. 
long. 70° 30', approximately, 
40 fathoms, sand and rocks, 
August 15, 1878) have these 
peculiarities to such an extent 
as to deseiTc special mention. 
In them, the spicules are con- 
fined chiefly to the upper lay- 
ers of the colony and are 
comparatively few, in some 
cases so few diat their pres- 
ence is not noticeable without 
the aid of the microscope. The colony is therefore quite translucent, 
being more like that of Didemnopsis in consistency. Their spicules 
(text-fig. 14) are variable in size and but few of them exceed 0.05 nun. 
or 0.06 mm. in diameter. INIanv of them, especially the smaller ones, 
have the points very short and more or less irregularly developed; in 
extreme cases the points are so reduced that they are mere rounded 
elevations on the surface of the nearly spherical spicule. AVith only a 
small series of specimens at hand, such colonies might be taken for a 
difTerent species. 
Mention should also be made of the fact that in this, as in some 
other members of this family {Lepfoclinides faeroends Bjerkan, for 
instance), closely crowded groups of small spicules occupying depres- 
sions on the sides of the outer wall of the thorax of the zooid may occur. 
The zooids in this species measure 1.5 mm. or 1.6 mm. or more in 
Text-fig. 14. — Tetrad idemnum albidum (Ver- 
rill). Irregular spicule.? from a colony from 
U. S. F. C. Station 157 (off Cape Ann, Mass., 40 
fathoms). X 340. 
