GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 403 



1870. Isastraea turbinata Duchassaing, Kev. Zooph. et Spong. Antilles, p. 31. 

 1902. Orbicella cellulosa Yavgsa^s , Geol. Soc. London Quart. Journ., vol. 52, p. 497. 

 1915. Orbicella cellulose Vaughan, Carnegie Inst. Washington Yearbook, No. 

 13, p. 360. 



Original description. — "Corallum tall, and, judging from the dis- 

 position of the corallites, subplane above. Coralhtes very numerous, 

 tall, slender, crowded, but distinct; usually cylindrical, but some- 

 times more or less prismatic from mutual pressure; varying in size. 

 The transverse section of the corallites is generally circular, now and 

 then deformed. Septa crowded, linear; the primary are the largest, 

 but often the secondary are nearly as large. The primary septa are 

 of nearly the same thickness at the wall and throughout. There are 

 six systems of four cycles; in imperfectly developed systems the 

 fourth cycle is wanting, but the persistence of this C3^cle throughout 

 all the systems is very generally decided. The fourth and fifth 

 orders are very small, and when there are only three cycles, the third 

 order is small; the septa are generally straight. Columella small and 

 slightly developed. The wall appears to be stout. Costae attached 

 to every septum, subequal, and not very greatly developed. Endo- 

 theca vesicular, greatly developed. There are often four dissepi- 

 ments dividing each interseptal space. Exotheca cellular and highly 

 developed; exo thecal cells small, more rectangular and larger than 

 the endothecal cells. The reproduction is by extracalicular gemma- 

 tion; the smallest buds visible have three perfect cycles of septa. 



''From the Conglomerate of Antigua. Coll. Geol. Soc. 



" Dimensions. — Height of corallum several inches. Diameter of 

 corallites from 1-2 lines [2 to 4.2 mm.]." 



The type of the species was examined in the collections of the 

 Geological Society of London, and the identification of the specimens 

 I am referring to it was verified. 



As this is an enormously variable species further discussion of it 

 should begin with a clear statement of the characters of the typical 

 form. These may be summarized as follows: Calices 2 to 4.2 mm. in 

 diameter, crowded, but distinct; costae subequal, not greatly devel- 

 oped; wall stout. Septa in four cycles, primaries the largest and of the 

 same thickness throughout; secondaries annost as large as the pri- 

 maries; tertiaries and quaternaries smaller according to cycle. Colu- 

 mella said to be small and slightly developed. Endotheca and exo- 

 theca greatly developed. Plate 98, figures 3, 3a illustrate a typical 

 specimen, which completely satisfies the requirements of Duncan's 

 description, except that close inspection shows a small, well-developed, 

 lamellate columella. Plate 100, figures 1, 2, are reproduced from 

 photographs of thin sections of specimens and show the lamellar 

 columella. 



The first variant to be considered is represented by plate 99, figures 

 1, la. The corallites have free limbs as much as 1.25 mm. tall, and 



