DIASTOPORA PATINA. 459 



radiating lines, towards the margin usually erect, open, 

 sometimes connate, sometimes disjunct ; orifice in the 

 central cells subelliptical, plain, in the marginal cells 

 suborbicular, often produced at one side, or bifid ; the 

 edge of the celliferous portion of the zoarium sometimes 

 gemmiparous. 

 Disk in ordinary specimens about ^ inch in diameter. 



The zoarium in this species, which is liable to many 

 variations in shape, due to the nature of its site, is met 

 with in two very distinct conditions. In one of them it 

 is decidedly caliculate, the cup being of greater or less 

 depth, and is as a consequence only partially adherent. It 

 is attached by the centre of the basal lamina, which is 

 otherwise free, usually rising above the celliferous centre 

 of the colony, and forming a thin, semitransparent wall 

 around it. In this form the marginal belt of erect and 

 open zooecia is generally well developed ; but there 

 is no uniformity in this respect, and in many cases 

 almost all the cells in the colony are closed and entirely 

 immersed. 



The rule, however, holds good universally that the open 

 cells, when present, occupy the marginal portions of the 

 zoarium. 



The zooecia are thickly punctate, and the puncta are 

 present on the calcareous lid or operculum, which closes 

 the orifice in a large proportion of them. The edge of 

 the zoarium is somewhat thickened and cellular. In many 

 cases the cup is deep and funnel-shaped, expanded above, 

 and narrowing off to a fine point below (Plate LXVI. 

 fig. 6) ; but it is very commonly shallow and depressed, and 

 attached by a larger portion of the basal surface. This 

 condition makes an approach to the second of the forms 

 which the zoarium assumes in this species. In the latter 

 the lamina is entirely and closely adherent, forming a 



