VAN NAME: COMPOUND ASCIDIANS. 397 
cases this is lacking. Tlie interior of the colony is comparativel}' free 
from sand. The zooids are in some specimens arranged in small 
circular or elliptical systems of from six to eleven zooids (usually about 
eight) ; in the center of each system a small roundish common cloacal 
orifice is more or less distinctly visible. In some colonies no such 
systems are discernible, the zooids being irregularly distributed. This 
character probably depends rather on the stage of growth of the colony 
than on individual variation or poor preservation. 
The three colonies of this species (all from the Banks of Newfound- 
land) which are in the collections have the following dimensions and 
characters : 
The smallest (the type of Verrill's genus ]\Iacroclinum and species 
M. crater) is of circular outline, about 45 mm. in diameter and 25 mm. 
in height. It was attached by a small area at the base and has 
the upper surface conspicuously concave, whence the name crater. 
Another, the most regular in form (PI. 38, fig. S), measures about 
115 mm. by 95 mm. in its transverse diameters and 95 mm. in height. 
It is attached to a stone by a very short stout peduncle, if indeed it is 
proper to apply that term to such a short thick extension of the colony. 
The third colony is 136 mm. in greatest diameter, though from its 
irregularity it is not of much greater bulk than the last. It was at- 
tached directly by a small area on the lower surface. Still larger 
colonies are reported by Hartmeyer from European waters. 
In one of the larger specimens, the zooids are beautifully expanded. 
In these, the thorax and abdomen together measure about 10 mm. in 
length, but in the usual contracted state are of l)ut half that length or 
less. The post-abdomen (the length of which is less affected by the 
contraction of the muscles) may itself measure fully 10 mm. in length. 
The muscles in the mantle form a network in which most of the fibers 
are longitudinal, but on the thorax a considerable number of oblique 
fibers and a few transverse fibers occur. The branchial orifice has 
six obtuse lobes. The atrial orifice is at the end of a short funnel- 
shaped tube situated well forward on the thorax, and is smooth- 
margined, with the anterior part of its border produced into a short 
languet, ending in three small finger-like processes. 
The tentacles, which appear to number about 12, are of two sizes 
placed alternately. The branchial sac has about 20 rows of moderately 
long stigmata. The number in a row on each side reaches 30 or even 
more. The stigmata begin close to the median dorsal vessel and ex- 
