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BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



are separated by intercorallite areas usually about 1 mm. wide, range 

 in width from 0.5 to 1.5 mm. The walls are thick; costae slightly 

 tleveloped, thin. Calicular diameter from 3 to 5 mm. Septa m 4 

 complete cycles; 6 thick primaries which reach the columella; sec- 

 ondaries stout, but thinner than primaries, reach to or almost to the 

 angle formed at the inner ends of the adjacent primaries; tertiaries 

 thin, their inner ends project just beyond a peripheral zone of dissepi- 

 ments; quaternaries small and thin, their inner ends barely reach the 

 inner side of the dissepimental zone. Columella a compressed axial 

 tubercle or an axial lamella. Endotheca and exotheca well devel- 

 oped. This specimen, which differs only shghtly from the typical 

 form of the species, represents the extreme of variation in one 

 direction. 



One line of variation from the typical form of the species is by 

 increase in the size of the calices, diameter from 7 to 9 mm., with 

 consequent greater development of the higher cycles of septa, and 

 the development of thin corallite walls which are separated by inter- 

 spaces from 1 to 2 mm. wide. The intergradation between speci- 

 mens with the large and small calices and thick and thin walled 

 corallites is complete; in fact, the variations may be found on the 

 same specimen. These larger calicled specimens belong to what 

 Duncan designated var. curvata. 



Specimens showing the variations so far discussed occur in Antigua 

 at the southwestern foot of the limestone hills from Willoughby Bay 

 practically to the intersection of the hills with the sea near Wetherell 

 Point. 



Other lines of variation may best be presented by describing a 

 series of specially selected specimens. 



Specim.en No. 1 , from. Station 6866, opposite the Cathedral, St. John, 

 Antigua (pi. 99, figs. 2, 2a). — Corallum broken on the base; 66 mm. 

 long, 50 mm. wide, 34 mm. tall. There is one tuberose protuberance. 



Corallites separated by narrow intercorallite areas, only 0.25 mm. 

 wide, or by areas which range up to 3.5 mm. across, measured between 

 the peripheries of neighboring calices. Where the calices are sepa- 

 rated the intercorallite areas are depressed and are crossed by thin 

 cbstae, which are confluent where they can be clearly seen, but in 

 other areas they may alternate; about 15 costae to 5 mm., or the dis- 

 tance between summits of adjacent costae is about 0.3 mm. ; the inter- 

 spaces decidedly wider than the thickness of the costae. 



The following table gives the size of eight calices. 



