GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 381 



placed in the synonymy of 0. cavernosa, has the general appearance 

 of Orbicella, but it is a fungid coral and is referred to the genus 

 CyathomorpJia. Astraea antillarum, given by me as doubtfully a 

 synonym of 0. cavernosa, should for the present at least be treated 

 as a valid species. 



As so many of the species related to 0. cavernosa must be con- 

 sidered in this paper, it is desirable to describe all those members of 

 the group found in the American Tertiary formations and now 

 living in the western Atlantic Ocean. The systematic rank of the 

 forms described on the following pages is open to debate, and I wish 

 here to express my recognition of other methods of treatment. As 

 the forms, whether they be designated "species," "subspecies," 

 "variations," or merely "variants," exist, and as they have geographic 

 and geologic significance, they should be discriminated and char- 

 acterized. In comparison with these desiderata nomenclatorial 

 considerations are of secondary importance. 



Orbicella cavernosa is so variable that great difficulty has been 

 experienced in constructing an intelligible description. A very 

 interesting specimen, obtained by Prof. J. E. Duerden in Jamaica 

 and presented by him to the United States National Museum, will 

 first be described in detail, as it shows within itself a wide range of 

 variation and indicates the lines of variation of other specimens 

 more constant in their character (see pi. 87, figs. 1, la, lb, Ic). 



The corallum is oblong; upper surface convex but not uniformly 

 arched or domed; base epithecate. Length, 25 cm.; breadth, 20 

 cm.; thickness, 11.3 cm. 



The specimen has two different kinds of calices. Those of one 

 kind are rather distant, protuberant, and have subequal, not very 

 tall, thick, dentate costae (pi. 87, fig. 1). The transverse outline is 

 circular or broadly elliptical, diameter between thecal summits 

 8 mm. ; one of the elliptical calices has a greater diameter of 11 mm., 

 lesser about 9 mm. The costae are about 1 mm. tall. The distance 

 apart, measured between the outer costal edges, is from almost 

 contiguous to 6 mm. The free limb of the corallite is subcylindrical 

 and projects between 6 and 7 mm. The calices, as is shown by 

 plate 87, figures 1, la, are not uniformly distributed, and vary in 

 size, form, and prominence. 



In a fully developed calice there are 48 septa, every other one 

 extending to and fusing to the columella. All the septa, particularly 

 the principals, are rather thick. The margins are dentate, within 

 the calicular cavity, they fall abruptly to the bottoms of the calices, 

 which are 3 to 4 mm. deep, and there the principals extend to the 

 columella. There are septal teeth around the periphery of the 

 columella but they are not in the form of well-developed pali or 

 paliform lobes. 



