STRUCTURAL FEATURES OF THE GENUS. 259 



species. The base may be acute or obtuse and provided with an attach- 

 ment sear. The outer calicinal margins are, typically, horizontally ex- 

 panded and at times more or less rerlexed. The size varies with the age 

 and species, in C. magnifiewm attaining a greater diameter than in any 

 other known simple coral. Fragments have been found which belonged 

 to specimens not less than 22 or 23 cm in diameter. The single speci- 

 men upon which this species was founded had a diameter of 16.5 cm 

 and an estimated length of 11.5 cm. 



Outer Covering. — Owing to the peculiar formation of the septa there is 

 neither necessity nor opportunity for the formation of a true wall such as 

 exists in typical rugose corals. A simple, protective, epithecal covering 

 Avas secreted and deposited by the'"randplatte," or that portion of the 

 polyp projecting over the edge of the calyx. This covering conforms to 

 all the regularities and irregularities of the corallum itself, shows the 

 ordinary circular accretion ridges of growth, and is longitudinally striated 

 with narrow grooves and broad fiat or concave bands, gradually increae- 

 ing in width from the base toward the edge of the calyx. These grooves 

 mark the position of the interseptal cavities and the broad bands the 

 position of the septa themselves. Thin sections show that the epitheca 

 is in contact with the under concave surface of the septa only here and 

 there, and that it receives its support mainly from the ridges produced 

 by the downwardly deflected edges of the series of layers which form 

 them. Owing to this loose connection with the body of the corallum the 

 epitheca is, in many specimens, either partially or completely lost, perha ] >s 

 from marine or atmospheric agencies. In consequence, decorticated forms 

 are somewhat characteristic of the genus, and it was this fact which led 

 the founders to assert the absence of wall rather than any real knowledge 

 of the outer covering which the} 7 were able to obtain from their limited 

 number of specimens. In all recognized species, radicinal and spinulose 

 processes are absent. 



< 'iilj/x. — The calyx is generally spacious and deep in comparison with 

 the height of the corallum. In some forms, however, it may be shallow 

 and basin-like; in others there is an abrupt and deep central pit. with 

 nearly vertical sides and broadly expanded margins. The outer edges 

 may be horizontally explanate or reflexed upon one or all sides. The 

 fovea is entirely absent or it exists only in the most rudimentary condi- 

 tion. The bottom of the pit is in general fiat, never smooth, but in one 

 species (C ponderosum) a distinct elevation may be formed by the twist- 

 ing together of the primary septa. 



Septa. — The original specimen of Goldfuss contains 76 septa; in C. 

 magnifiewm they range from tins number to L20 in mature specimens,, 

 while in C. 'ponderosum they may reach 1 I". In the specimens of Edwards 



