GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 473 



"In young corallites there are six systems of three cycles. As 

 growth proceeds the other orders of the fourth and sometimes of the 

 fifth cycle are gradually added. Some systems are defective in 

 certain orders, while others possess them. The largest corallites 

 have four perfect cycles, and a fifth in two or three systems; the 

 ninth order being usually wanting. It is difficult, in the larger 

 corallites, to distinguish the systems on account of the resemblance 

 of the primary, secondary, and tertiary septa to each other. 



"The primary septa are very thick externally, but delicate and 

 linear elsewhere; the linear part joins the rest suddenly, like the 

 staff of a big-headed spear; at the junction the thick corners of the 

 enlargement give off a lateral spine, like a piece of endotheca; near 

 the costal end of the septa there are delicate lateral spines. The 

 space between the sets of lateral spines is more or less square. The 

 secondary septa are very like the primary. 



"When there are more orders in the system than five — that is, 

 when there are six, seven, eight, and nine — the tertiary septa equal 

 the primary and secondary, the blunt end terminating in the linear 

 portion a little nearer the wall. When there are four cycles, the 

 tertiary septa are smaller than the primary and secondary; and when 

 there are only three cycles, as in young corallites, the tertiary septa 

 are linear throughout. The quaternary septa are linear and very 

 slightly developed; when there are more septa than those of the fourth 

 cycle, the quaternary resemble small tertiary septa. The remaining 

 septa are very small and linear, and reach a very little way from the 

 wall; they are apt to curve towards the septa nearest them. In 

 examining the shape of the septa in this and in all the allied forms, 

 particular attention must be paid that the section is quite transverse, 

 as any obliquity will more or less alter the shape of the larger end. 



"As regards the endotheca, the dissepiments are frequent and 

 delicate, and not very much developed. The exotheca is tolerably 

 well developed, but not in proportion to the size of the corallites. 

 Its dissepiments form square cells. The free surface between the 

 costae and calices has a few granules. Increase by extracalicular 

 gemmation. 



"Marl formation of Antigua. Coll. Geol. Soc. 



" Measurements. — Diameter of the calices in six specimens f inch 

 [19 mm.], in seven others f inch [20 mm.], and in some from § to | 

 inch [12.5 to 6.25 mm.]. The elliptical calices (situated on the sides 

 of the corallum) are about 1-^ inch [27.5 mm.] in longest diameter. 

 The greatest thickness of the septa at the wall is -^ inch [2.5 mm.]. 

 Columella ^ inch [5 mm.] in diameter." 



It is obvious that Duncan had no really good specimens on which 

 to base his original description of this species. I was fortunate in 

 obtaining more than 60 specimens in Antigua, and have selected 14 



