338 R. M. Brydone—New Chalk Folyzoa. 



by Marsson's figures aud description ^ (Hagenow's figures and 

 descriptions being inadequate), it is easily distinguishable by the 

 shape of the aperture. 



HoMALOSTEGA BicoNVEXA, uov. PI. XIV, Figs. 3 and 4. 



Zoarium resembling that of H. anglica. 



Zooecia tumid, but less so than those of H. anglica. A.perture sub- 

 terminal, biconvex ; upper lip semicircular, lower lip very faintly 

 curved outwards in the centre, more so at the sides ; shallow slits in 

 the corners. 



Avicularia accessory, very abundant, with broad rounded bodies and 

 rapidly tapering pointed beaks which are generally bent round the 

 head of a cell ; aperture occupying the greater part of the area, spanned 

 by a bar ; when this is broken away the aperture is arrowhead -shaped 

 or diamond-shaped. They lie almost invariably at a distinct angle to 

 the lines of growth and often in pairs, one on either side of a cell and 

 almost meeting round its head. 



Ooecia not observed. 



Abundant at Trinimingham. 



HOMALOSTEGA VESPEKTILIO, Hag. sp. PI. XIV, Fig. 5. 



Neither Hagenow ^ rtor Marsson ^ appears to have observed vicarious 

 avicularia in this species. It is very abundant at Trimmingham, and 

 though most colonies, including some of the largest, show no vicarious 

 avicularia, in some they occur capriciously, and I have figured part of 

 a colony in which they are exceptionally numerous. They may be 

 described as ordinary zooecia of which the apertures have been drawn 

 out to a great length. 



The species is very prone to occur as a free unilaminate sheet 

 separated by a very thin layer of chalk from the surface of some fossil. 



HoMALosTEGA cuNiFORMis,^ uov. PL XIV, Figs. 6 and 7. 



Zoarium unilaminate, generally adherent. 



Zooecia very large ; irregular growths, to which this species is very 

 prone, often simulate fragments of a dividing wall, or make two cells 

 apparently confluent. Aperture subterminal, semicircular ; the lower 

 lip has a broad raised rim ; the upper lip rises rapidly from the lower 

 lip owing to the strong inflation of that part of the cell which surrounds 

 the upper lip, making it stand up like the hood of a cradle, and it 

 thickens as it rises. 



Avicularia intercalated as initial cells of new lines. Relatively 

 narrow, highly inflated with a central circular aperture from which 

 runs a long, slightly tapering, symmetrical beak consisting of two side 

 walls enclosing a slightly depressed front wall, which at the tip is 

 sharply expanded. 



Ooecia occurring very capriciously, very globose.^ 



Occurs sparingly, but in large colonies at Trimmingham. 



1 " Bryozoea der "Weissen Schreibkreide der Insel Rugen " : Pal. Abb., Baud iv, 

 Heft i, p. 93. 



* Neues Jahrbuch fiir Mineralogie, etc., 1839, p. 270. 



2 Op. cit., p. 94. * From cimtB, a cradle. 



* The free edge produced over the aperture of the zoarium. 



