412 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
the calices opening in all directions. Tubes expanding rapidly 
towards the calyx, below which they give off one or more lateral 
buds. Adjoining corallites frequently united by their walls. 
Walls thick, especially in the lower portions of the corallite, con¬ 
sisting of numerous concentric lamellae, between which the reticu¬ 
late structure appears. The lacunae are subequal, but the lamellae 
separating them are more irregular, and as a rule thicker than those 
of M. crassa. The trabeculae are also more irregularly disposed. 
This species differs from the described and figured forms of M. 
crassa in the larger size of its corallites, the more confused growth 
of the agglomerated masses, and the greater length and more 
regular budding of the simple branches. The internal differences 
appear to be the irregularities of the reticulate tissue, which is also 
much less frequently developed. From M. antiqua it differs chiefly 
in the surface features, and in the thickness of the wall, which in 
that species is stated to be “rather thin.” 
This species, like the European M. crassa, frequently grows 
around crinoid stems. It is commonly found on the stems of Platy- 
crinus, which is an abundant genus in the rocks in which this coral 
occurs. When thus attached, it takes on a surprisingly irregular 
colonial form, calices budding out on all sides. In one of the speci¬ 
mens figured (PI. 1, figs. 2, 3) the calices point upwards and 
downwards, as well as outwards in all directions. This would seem 
to indicate that it grew on the crinoid stem while the latter was 
erect, and that the coral was attached around the stem at some 
distance above sea-bottom, thus allowing free expansion of the 
corallites in every direction. 
The regular coralla give off calices at definite intervals, these 
calices pointing upwards and outwards on all sides. From this it 
appears, that the regular coralla grew upright, unsupported except 
basally (PI. 2, figs. 1-3). The more usual method of growth, 
however, seems to have been by irregular budding, which resulted 
from the attachment of the young coral to the crinoid stem. Such 
an attached individual would not require the regular growth, which 
is necessary in the free corallum to maintain proper balance, and 
hence the attached corallum can put out buds promiscuously. 
With increasing age, the individual corallites become separated 
from each other internally, by the extension of the sclerenchyma 
over the pore through which the young polypite was connected with 
the parent. 
