﻿160 Proceedings of the Royal Physical Society. 



tapering towards the apex. Base of attachment not known. 

 Surface without monticules or maculae. Zosecial apertures 

 subcircular, separated by thin interspaces, from twenty-five 

 to twenty-seven in the space of 1 cm. The interspaces are 

 occupied by two sets of acanthopores ; a relatively large 

 acanthopore can generally be seen at the junction angles, 

 whilst smaller ones, numerous and regularly distributed, 

 surround the zosecial apertures. As seen on longitudinal 

 fractures, the zoaecia, in the mature region, are perpendicular 

 to the surface, but that portion of their course does not 

 exceed 1 mm. in length. Constrictions corresponding to 

 swellings of the walls are visible with the aid of a lens. 



Microscopical Examination. — Walls thin in axial region, 

 but very much thickened in the mature one; the swellings, ' 

 numbering only five or six, have a somewhat conical shape, 

 the base of the cones being parallel to the periphery. Tan- 

 gential sections show a large aca,nthopore at the junction 

 angles between the zosecia, which are also surrounded by 

 a ring of smaller acanthopores. The latter are not so sharply 

 defined as the larger ones, that is, their shape is not so 

 perfectly cylindrical. N'o diaphragms could be detected in 

 any part of the course of the zosecia. 



Eemarks. — So far as one can judge from the material at 

 hand — which amounts to about thirty fragments — the zoarium 

 in this species appears to be always simple, i.e., not made up 

 of concentric layers of superimposed colonies. 



Affinities and Differences. — S. cidariformis differs from 

 S. hrucei in the fact that it has two sets of acanthopores, 

 zoaecia shorter in the mature region, with a different wall- 

 structure, and a zoarium of more slender habit. A character 

 that these two species have in common is the absence of 

 diaphragms. As already stated, this feature has been observed 

 in three American species, but the latter are otherwise quite 

 different. Stenopora (?) signata, Ulrich, has a peculiar wall- 

 structure, not distinctly moniliform ; S. angidaris, Ulrich, is 

 extremely massive, w^ith very thin walls in the mature region, 

 whilst the species described by Mr Eogers shows no monili- 

 form structure of the walls. 



Stenopora crassa, Lonsdale, as understood by Lonsdale 



