278 
BULLETIN" 106, UNITED STATES NATIONAL MUSEUM. 
the cryptocyst is smooth, slightly convex. The aperture is semilunar, transverse; 
the proximal border is straight with two small lateral slits. The zooecia of the 
internal lamellae have a granulated crvptocyst and their apertures are closed by 
a calcareous lamina. Five dietellae are present. 
Variations. — This species is a true Macropora / the aperture does not occupy 
all the distal extremity and is provided with a decided peristome and a small 
vestibular arch; the zooecia are exactly hexagonal; there are five dietellae. 
The granular constitution of the inner zooecia is quite remarkable. These 
granules are equivalent to the “hydrostatic tuberosities;” their object is to keep 
the upper zooecial lamella at a distance to avoid an intimate contact analogous to 
that of other multilamellar bryozoa. They are secreted by the endocyst which 
floats in the hypostege (Calvet) and forms a special pleurocyst. These zooecia 
were without polypide, since their aperture was closed by a calcareous lamina 
secreted by the endocyst; but they might have continued to live, to be traversed 
by the mesenchymatous filaments of the endocyst, since the granulations are formed 
only at the moment of the formation of the upper lamella. 
The zoarial unity of the bryozoa is incontestable since the larva is unique, but 
it often manifests itself in a rather obscure fashion in the incrusting species. 
In the present instance it appears as if a real intelligence presided over the vital 
manifestations at the moment of their necessity. 
The utility of the frontal granulations is not evident at first glance, but it is 
easy to find their explanation by examining the whole of the zoarium. The granules 
are really hydrostatic and are also designed to augment the volume and the lightness 
of the zoarium. The larva affixes itself to sand grains, over which the zoarium 
spreads rapidly. This is a very dangerous habitat, as the sand is in danger from 
the least movement of the water. To avoid this the animal multiplies its lamellae, 
preparing for itself in this way its own foundation; by the specific lightness thus 
acquired it may have the power to elevate itself above the sand and avoid this 
dangerous zone. It is evident that the zoarium is entirely surrounded by the 
ectocyst and that the disruption of this would impede the working of the hydrostatic 
At the bottom of each zooecium there are two oblique, projecting lamellae 
which serve as supports for the upper lamella. 
Affinities.- — We have not found an ovicell, and in spite of its appearance this 
species is not a Ooscinopleura. It differs from Macropora centralis MacGrillivray, 
1895, and from Macropora clarkei Tenison Woods in its frontal tuberosities and in 
its multilamellar zoarium. These two species are from the Miocene of Australia. 
The genus Macropora is unknown in Europe. However, in the English 
Cretaceous there is Homolostega cuniformis Brydone, 1900, which may be either 
a Macropora or a C oscinopleura , but of which the ovicell is not yet known. 
Zooecia 
Zs=0. 85-0.90 mm. 
Zs=0.65-0.75 mm. 
system. 
