176 RECENT MADREPORARIA OF THE HAWAIIAN ISLANDS AND LAYSAN. 



The ciiliccs arc polyj^onal, scparatvil hv ilctiiiitc, continuous walls. Tlio range 

 in diameter is from slightly less tluin 1 mm., the smallest caliees on some specimens, 

 to about 2.25 mm., the largest caliees on other specimens. The average diameter 

 for sjiecirnens ranges from about 1.4 to about 1.75; probably 1.5 mm. is the average 

 for the species as a whole. The depth of the ealices is \ariable, from superficial to 

 deep. 



The se])ta vary much in thickness. There is usually a single trabecula between 

 tiie palar and mural trabecuhe, emei-ging on the septal margin and producing a septal 

 granulation. Near the lower edge of the living portion of the colony and where 

 calict's have pi-olonged corners, freijuently there are two trabecular between the palus 

 and tlie wall, which correspondingly produce two graiuiles on the septal margin. On 

 some specimens many or most of the septa are composed of two septal trabeculte. 

 These trabeculie, when tliere is only one ring, or the outer septal trabecula when 

 there are two, are more or less coiupletely united by a ring of synapticula. The 

 septal trabecule next the wall and their circular connections mayor may not produce 

 a mural shelf. 



The pali are alwaj's distinctly developed, and the formula is normally complete; 

 that is, there are 8 pali. Occasionally the palus is suppressed on the dorsal directive, 

 and frequtMitly there is variation in the triplet; the ventral directive is often shorter 

 than the laterals of the triplet, and the palus on it may be obsolete. The pali are 

 nearly always united l)y a ring of synapticula. 



The columella is a compressed stvle, joined by radial connections to the inner 

 terminations of the septal groups. 



The skeletal surfaces are always granulate or frosted, with considerable variation 

 in the thickness, length, shape, and proximity one to another of the granulations. 



The preceding description will show that there is a fundamental scheme under- 

 lying all of the variations and that each structural element is variable, but the varia- 

 tion is within limits. In defining the variations subsequently described, the following 

 factors are taken into account: 



1. The form of the corallum, which is considered of minor importance. 



2. The size of the calices. 



3. The depth of the calices. 



4:. The character of the wall, particularly the muial denticles. 



5. The number of the septal trabecuhe between a palus and the wall, and the 

 dentations or granules on the septal margins. The relation between the granule next 

 the wall and the wall is of decided importance. 



6. The pali, especially tlie tendency to deviate from the complete formula. 



7. The synapticular rings, whether complete or incomplete, and the degree of 

 fusion with, or aloofness from the wall. 



8. The columella. 



9. The character of the granulation or frosting of the skeletal surfaces. 



