50 ',Mr. H. J. Carter on the close Relationship of 



after this it should be remembered that this regularity is by 

 no means persistent throughout the skeleton, but, on the con- 

 trary, subject to great latitude in point of modification and 

 irregularity. When, therefore, the regularity may be found 

 almost persistently in the structure of some species of Stroma- 

 topora^ it is no indication that they were hexactinellid sponges, 

 but, on the contrary, that they were something else ; for I have 

 never seen the hexactinellid structure in sponges so' persis- 

 tently regular as in these species of Stromatopora. 



Calcareous Hydractiniid^. 



Let us now direct our attention to the structure of the skele- 

 ton in the calcareous species from Cape Palmas, which, hitherto 

 having been undescribcd, will be given under the designa- 

 tion of " calcarea.^'' 



Hydractinia calcarea, n. sp. (PI. VIII. figs. 4-6.) 



Skeleton laminiform, incrusting, spreading, cancellous, mas- 

 sive, not reticular, stony coral-like. Composition calcareous. 

 Colour greyish white. Surface rough, spiniferous : spines at 

 the growing margin commencing in minute points of cal- 

 careous matter scattered through a sarcodic lamina of almost 

 immeasurable thinness, arranged more or less linearly so as 

 to resemble a furrowed area, afterwards becoming thicker and 

 rising into conical points, which, uniting more or less together, 

 form serrulated lines that are rendered irregular in height by 

 some points being higher than others (fig. 4, a, d) ; finally 

 developing another lamina (fig. 4, c), which is supported on 

 some of the small spines of the first, and which, in its turn, 

 also throws up similar spines on its surface (fig. 4, e). Upper 

 lamina much thicker than the lower one, having an irregular 

 interval between them (fig. 4, d) about 1-1 80th inch high, 

 which in the vertical section presents a number of arched 

 cavities formed by the small spines of the first or basal lamina 

 uniting, in the form of pillars of support, with the under- 

 surface of the second or surface lamina, leaving some of the 

 spinulse still free on tlie floor of the arclied cavities. Skeleton 

 (fig. 4) seldom if ever formed of more than two laminae. 

 Surface of the upper lamina ridged reticulately ; ridges com- 

 pressed, serrulated irregularly with small spines, interrupted 

 at irregular distances by large ones (fig. 5j aaa^hbh, small 

 spines omitted in the illustration for perspicuity) ; interstices 

 pit-like and without spines (fig. 5, ddd). Large spines 

 about l-60th inch high (fig. 4,/, and fig. 5, a a a), variable 

 in shape, round or compressed, hollow in the interior (fig. 4,/, 



