268 Professor E. J. Garwood — ■RocJc-huilding Organisms. 



probably algae, but too imperfectly known to be referred to any 

 particular family." ^ 



Aphralysia,- gen. nov. (PL XXI, Figs. 3, 4.) 



The macroscopic characters of this organism can only be generally 

 inferred, as specimens have not been isolated from the matrix. In 

 translucent sections of the rock, however, these organisms are seen 

 to occur as thick incrustations surrounding fragments of various 

 organisms and, if isolated, they would appear as small nodules up to 

 10 mm. in diameter, having a slightly lobulate surface, thus resembling 

 nodules of Girvanella or Solenopora. 



Under the microscope the nodules are seen to be built up of a series- 

 of semicircular and semi-elliptical plates arranged in irregular 

 alternating rows, having the convex surfaces of the plates directed 

 uniformly outwards away from the centre of growth, giving a general 

 appearance of wreaths of bubbles, encrusting fragments of shells, or 

 the thalli of Ortonella and other algal forms. The growth usually 

 starts with small plates resembling hollow blisters attached by their 

 edges to the surface of the object which serves as a nucleus. 

 The size of the blister-like cells increases in the succeeding row, 

 and usually averages •12 mm. in height in the centre. The length 

 of the cells varies according to the position of the sections, but 

 the height of the arch is remarkably uniform in the majority of 

 cases, whatever the length of individual cell. These curved plates, 

 bounding the outer surfaces of the cells, sometimes occur as very 

 thin dark lines, but they are more frequently represented by a pale 

 orange-coloured film or stain. This colouring matter may extend 

 inwards so as to occupy a quarter or even a third of the cavity, the 

 thickness depending apparently on the angle made by the wall with 

 the plane of the section. There is a complete absence of circular 

 sections, so that the cells cannot be tubular in character. The 

 structure is thus shown to consist of a series of alternating rows of 

 elongated, highly arched plates, each plate resting with its edges 

 supported by the plates of the row below, exactly like a tangle of 

 soap bubbles or a mass of foam. 



No other definite structures can be made out, but occasionally in 

 sections cut tangentially to the surfaces of the nodules a few curved 

 plates may be observed (exactly similar in structure and colour to 

 the boundary walls) which appear to divide up some of the more 

 elongate cells. These may, however, be the edges of other cells cut 

 by the plane of the section. This organism is frequently intergrown 

 with layers of a flocculent deposit which may be classed under the 

 general term ' Spo^igiostroma '. 



The exact nature of Apliralysia is somewhat doubtful. Its 

 mode of growth and its intimate association with Ortonella and 

 ' Spongiosti-oma ' would appear to suggest algal affinities, but the 

 comparatively large size of its cells and their mode of growth 

 differentiate it from any examples of fossil calcareous algae known 

 from the Lower Palaeozoic rocks. 



^ Seward, Fossil Plants, voL i, p. 160, 1898. 



•^ ' Chain of foam.' From &cppos, ' foam,' and aXvcm, ' a chain.' 



