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 cryptocyst and their apertures are closed by 

 a calcareous lamina. Five dietellae are present. 



fha=0.12mm. , \ 2=0.85-0.90 mm. 



Measurements. Aperture -L ,_ Zooecia , ,. _,. 



\la= 0.17mm. Us=0.65-0.75 mm. 



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 

 system. 



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 C oscinopleura. It differs from Macropora ccntralis MacGillivray. 

 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. 



