290 ZOANTHARIA. 



laminae often become more or less zigzag in the peripheral part of 

 the corallum. 



As regards the other characters of the Heliophyllidce, the outer ends 

 of the septa terminate with apparent abruptness in a thin outer invest- 

 ment, which is not improbably rather of the nature of an epitheca 

 rather than of a true "wall.' In some cases {Phillips astrced) the 

 corallites have no definite outer investment, the septa of adjacent 

 tubes becoming confluent. As in the Cyathophyllidce, there is a 

 well-developed external vesicular zone, and a comparatively small 

 central tabulate area. The range of the family is from the Silurian 

 to the Carboniferous, but the great majority of the species are 

 Devonian, the group being, as a whole, as characteristic of the De- 

 vonian period as the family of the Clisiophyllidce is of the succeed- 

 ing Carboniferous period. The three leading genera are Heliophyl- 

 lum, Crepidophyllum, and Phillip sastrcea. 



In the genus Heliophyllum itself the corallum is simple (fig. 169) or 

 composite ; the carinate septa are numerous and alternately long and 

 short, the latter, however, being of considerable length ; and the longer 

 septa are, many of them, continued inwards to near the centre of the 

 visceral chamber, where they become twisted, and coalesce to form a 

 spurious columella, which is of large size, and often projects prominently 

 into the floor of the calice (fig. 168, a). The symmetry of the corallum is 



distinctly bilateral, a well-marked "fossula" 

 being present. The "cardinal septum" is 

 shorter than the other long septa, and, along 

 with two short septa, occupies the fos- 

 sula. The exterior vesicular zone is well 

 developed, dissepiments being exceedingly 

 abundant, and there is a small tabulate 

 central area (fig. 168, b). The species of 

 the genus are principally Devonian, but 

 some Silurian corals have also been re- 

 ferred here. The genus Heliophyllum has 

 commonly been regarded as a mere sub- 

 genus of Cyathophyllum, but if due weight 

 be given to the peculiar structure of the 

 septa, it can hardly be placed in the family 

 of the Cyathophyllidce at all. The genus 

 Fig. 169.— A young form of Helio- Crepidophylliun is in general structure es- 



SS£f"S*SsiSSSr{SS: se»« all y si ™ lar to ^w^.ta the 



ginal.) central tabulate area is enclosed in a dis- 



tinct accessory wall or inner mural invest- 

 ment, which is usually open on one side so as to communicate freely with 

 the large fossula (fig. 128, b). The corallum may be simple or compound, 

 and all the known species of the genus are found in the Devonian rocks. 

 Lastly, in the genus Phillipsastrcea ( = Smithia) the corallum is com- 

 pound, and the internal structure of the corallites is essentially the same 

 as in Heliophyllutn. 1 The corallites, however, are devoid of a wall, and 



1 This statement is based on a microscopic examination of Phillipsastrcea 

 irneuilli, of the American Devonian rocks, the type-species of the genus. 



