Polytremacis and the Ancestry of Helioporidce. 293 



teeth j in the coral figured by von Eeuss, each calicle has from eight 

 to fourteen lamellar septa. The second difference is much less im- 

 portant, and consists in the more crowded arrangement of the calicles 

 in Michelin's type of the species ; but the distribution is not uniform 

 in Michelin's specimen, and varies enormously in a series of specimens 

 from the Tiu-onian of the Bouches-du-Ehone recently received by the 

 British Museum. The difference in the septa is, however, more signifi- 

 cant ; that the septa in some of the Gosau Polytremacis are lamellar is 

 shown by Lindstrom's own description of a specimen sent him from 

 Vienna. It does not seem to me necessary to regard the difference as 

 of generic value ; but it certainly seems reasonable to treat it as a 

 specific distinction, and I therefore propose to name the Gosau speci- 

 mens with long septa Polytremacis septifera. 



The type species of Polytremacis is therefore P. hlaimillei (Mich.) 

 no'n Eeuss. 



3. The Structure of Polytremacis. 



Caralhim. — The- corallum is irregularly lobed, or grows in thick 

 cylindrical branches. The whole surface is granulated. The calices 

 are crowded (P. blainvillei) or widely and irregularly separated (P. 

 jpartschi). The greatest separation is due to the closure of dead 

 calicles by growth of coenenchymal cseca (as in Heliolites interstinctus ; 

 Lindstrom, 9, Plate 1, fig. 21). This closure is illustrated by a figure 

 of two calicles of P. macrostomi (Plate 2, fig. 1). 



Thin sections show that the corallum is deeply excavated by large 

 cylindrical calicles, the walls of which are smooth or fluted. In 

 typical calicles the walls are thick; but young calicles and some 

 internal ones may remain in a thin-walled Heliopora stage (Plate 2, 

 fig. 3). The calicles are surrounded by narrow caeca, which are circular 

 €r elliptical in section. The caeca may be irregular in arrangement, or 

 occur in a circle round a calicle. Outgrowths from the caeca or from 

 the calicle traverse the caecal mass like canals. 



Septal Structures or " Pseudosepta." — The external rim of the calicle is 

 marked by an irregular series of granules forming septal teeth like 

 those of Heliopora, as, e.g., in Michelin's original figure of P. blainvillei. 

 These teeth may be continued down the sides of the calicles as con- 

 tinuous ridges, which may be few and long, as in P. septifera, or 

 numerous and short, as in P. blainvillei. The septal ridges may be 

 continued radially outwards ; on the surface they then appear as lines 

 of radial granules (Plate 2, fig. 1) ; internally, in thin sections, they 

 ^ippear as lamellae, continued outward as costal lamellae separating the 

 coenenchymal caeca. This arrangement is not shown in all sections ; 

 it is illustrated by Plate 2, fig. 4a. Lindstrom's figure of Plasmopm-a 

 suprema shows a similar structure [9, Plate 7, fig. 24]. 



In the older parts of the calicles the septal structures are absent 



