60 [Mr. IT. J. Carter on the closf Relationship of 



after tliis it should be remcnihered tliat tins regularity is by 

 no means persistent throug-liout the skeleton, but, on the con- 

 trary, subject to great latitude in point of modification and 

 irregularity. When, therefore, the refpdarity may be found 

 almost ])ersistcntly 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 1 have 

 never seen the hexactinellid structure in sponges so persis- 

 tently regular as in these species of Stromatopora. 



Calcakeotjs Hydkactiniid^. 



Let us now direct oin* attention to the sti-ucture of the skele- 

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

 having been undescribed, will be given under the designa- 

 tion of " calcarea.^^ 



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



Skeleton laminifonn, incrusting, spreading, cancellous, mas- 

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

 Colour greyish Avhite. 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 suppoi'ted on 

 some of the small sjiines of the first, and Avhich, 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 

 spinulge still free on the floor of the arched cavities. Skeleton 

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

 Surface of the upper lamina ridged reticulately ; ridges com- 

 pressed, serrulated iiTegularly with small spines, interrupted 

 at iiTCgular distances by large ones (fig. 5, aauj b bb, 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,f, and fig. 5, a a a), variable 

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



i 



