96 



Genus BOTRYLLOPORA (Nicholson). 



(Canadian Journal, Vol. XIV., No. 2, 1874.) 



Polyzoary calcareous, sessile and encrusting, forming systems of small circular discs, the 

 upper surfaces of which are marked with radiating ridges upon which the cells are carried. 

 Each disc is attached by its entire lower surface, slightly convex above, with a central non- 

 poriferous space, round which a number of radiating poriferous ridges occupy an exterior 

 slightly elevated zone. Cells forming a double series on each ridge, immersed, with rounded 

 mouths which are not elevated in any part of their circumference above the general surface. 



I have been unable to refer these singular Polyzoa to any existing group, and have, 

 therefore, been compelled to form a new genus for their reception. In some respects the 

 genus is allied to Defrancia, but the cells are not tubular, and no portion of them is free, 

 whilst the latter genus does not appear to have ever been detected in rocks older than the Ju- 

 rassic. The only Palaeozoic genus of Polyzoa which, so far as I am aware, presents even a 

 superficial resemblance to Botryllopora, is Evactinopora of Meek and Worthen. In this latter 

 genus the polyzosry is star -shaped, but its internal structure is quite peculiar and altogether 

 different to that of Botryllopora, whilst the entire organism appears to have been free. 



The individual discs of Botryllopora present, however, a very striking resemblance to the 

 separate star -shaped elevations of Stellipora antheloidca (Hall), from the Lower Silurian ; and 

 it may, therefore, be proper to say a few words on the structure and affinities of this genus, 

 of which I have examined authentic specimens. Stellipora antheloirfea occurs in the form of 

 flattened expansions or of erect, flattened and sub-palmate fronds. The surface exhibits a vast 

 number of little star-shaped elevations, each about a line in diameter, and consisting of a 

 smooth, sometimes slightly depressed space, which is traversed by five, six or more obtusely- 

 rounded radiating ridges, which do not quite meet in the centre. Each of the ridges of the star 

 is covered with a number of rounded calices, irregularly disposed in two, three or four rows. The 

 stars are arranged irregularly, generally at intervals of from half a line to a line, and the inter- 

 spaces between them are occupied by crowded circular pores, which are the mouths of so many 

 coenenchymal tubuli. These pores do not encroach upon the spaces between the ridges of the 

 stars, and the tubuli of which they are the mouths are seen on traverse section to be tabulate. 

 being furnished with distinct transverse partitions. It thus appears that Stellipora antheloidea 

 (Hall), is not a Polyzoon, as believed by D'Orbigny, but a tabulate coral, allied to Monticuli- 

 pora, and presenting in particular a specially close resemblance to the coral which I have 

 described under the name of Callopora incrassata. 



117. BOTRYLLOPORA SOCIALIS (Nicholson). 



Botryllopora socialis (Nicholson), Geological Magazine, April, 1874. 



Polyzoary social, consisting of systems of calcareous discoid bodies, which are closely 

 adherent by their lower surface to the exterior of foreign objects. The upper surface of each 

 disc is on the whole convex, but with a central cup-shaped depression or flattened space, the 

 exterior portion of each being occupied by a series of strong elevated ridges or ribs arranged 

 in. a radiating manner. The diameter of the discs is about a line or a line and a quarter, and 

 the radiating ridges are from eighteen to twenty-six or more in number. The radiating ribs 

 a-re also unequally developed, some extending much nearer to the centre than the others, and 

 each carries upon its upper surface a double row of minute round pores or apertures, the margins 

 of which are not elevated above the genera] surface. The central space of the polyzoary is des- 

 titute of cells, and appears to be solid, and this seems also to be generally the case with the 



spaces between the radiating ribs. In some cases, 

 however, the interradial spaces appear to be poriferous 

 in the immediate vicinity of the circumference. 



The groups of this singular 'Polyzoon are not of 

 very rare occurrence in the Hamilton formation, 

 growing parasitically upon the exterior of Heliophyl- 



Fi(r 32 lum Halli. It has at first sight, a close resemblance 



a. Portion of a coral with a small group of Botryi- to a group of little discoid corals, such as Microcydus, 

 lopom socialis (Nich.) of the natural size ; 6. A single attached bv the whole of the lower surface, the cellu- 



discoid polyzoary enlarged; c. One of the radiating ,.,, .%,,.. ,., , 1,1 



ridges, enlarged to show the cells. From the Hamil- UiCrOUS ndgCS looking JUSt like the Septa, and the 



:on group. central space resembling the bottom of the calice. I 







