CORALS FROM MURRAY, COCOS-KEELING, AND FANNING ISLANDS. I35 



Fronds crispate, summits divided into relatively narrow, more or less curled lobes. 

 Without carinae. 



Calices about 1 mm. in diameter. 



Ambulacra flat or only slightly convex. 



Septa subequal or only slightly alternating in size, except near the calicular fossa?; 

 columella distinct. 

 Fronds with narrow (2 to 3 cm. wide) acute, thin, twisted summit lobes *P. prcetorta Dana 



Fronds much wider (up to 12 cm.) and thicker, maximum thicknes s J„p cactus U' ursk -)- 



about 5 mm., thin on the edge, summit lobes I to 3 cm. wide. ..!*>,' {"""""J™"' 



l*y . knom (M. Edw. and H). 



Fronds wider and calices more distant than in P. cactus P. muelleri (M. Edw. and H.). 



Ambulacra flat. 



Septa strongly alternating in size. 



Polia intermediate in form between P. pratorta and P. formosa *P. venusta (Dana). 



With carina;. 



Ambulacra flat. 



Series about 3 mm. apart, columella compressed in direction of series; septa L*," , ax „ , 



strongly alternating in size ) • ^ axa "-' z ' 



' \*P. complanata Verrill. 

 Branches narrow, angular, keeled, twisted, and coalescent. 



Branches stout, 5-7 mm. thick, crowded, calices 2-3 mm. in diameter *P. divaricata Lam. 1 



Branches prismatic, 3-sided, sharply triangular, looser than in P. divaricata P. prismatica Brueg. 



Branches thin, foliaceous, many times bent, folded, and twisted, more numerous and more 



crowded than in P. divaricata P. minor Brueg. 



Externally like P. divaricata, except calices somewhat smaller, series more or less regular, sepa- 

 rated by sharp or obtuse ambulacra p. striata Brueg. 



Corallum massive. 



Corallum forming clavate columns; calices in indistinct series, 3 mm. in diameter; walls below thick, 



solid, flat; septa 3 cycles or more; columella a compressed, thick knob. . . "P. clavus Dana.' 



Corallum forming thick plates, or of irregularly tuberose form; calices forming indistinct series; 

 collines flat; calices 1.5 mm. in diameter; septa, 2 cycles; columella a single 

 papilla. *P. duerdeni Vaughan' 



Corallum thin and spreading at the base, with knobs and columns in the center; calices 2-4 mm. in 

 diameter, with flat or raised edges; 16-36 septa; columella well developed, a 

 twisted rod or a flat-topped, thick, or a pointed style *P. maldivensis (Gardiner).' 



Corallum forming large, heavy masses; calices 2.5 mm. in diameter forming indistinct series; collines 



flat (5 mm. from summit to summit across fossa) *P. giganlea Verrill. 



Corallum forming rounded masses; calices without distinct serial arrangement; 1.5 to 2.5 mm. 

 from wall to wall; septa, 2 cycles and some members of a third; columella a 

 compressed tubercle *p. clivosa Verrill. 



Corallum primarily incrusting, subsequently may become massive. 

 Upper surface hydnophoroid. 

 Columella often absent. 



Valleys 3 to 4 mm. wide; with single series of calices; septa to calice about 24, 6 to 8 



larger *p. varians Verrill. 



Columella distinctly developed, papillary. 



Diameter of calices 2 mm., septa 24 *P, ripens Briig.* 



Columella a small compressed spine. 



Primarily incrusting, becoming massive; ambulacra 3 mm. across; ridges thin above, thick 



below; septa from 12 to 60, according to size of calices *P. intermedia Gardiner. 1 



Separated from P. intermedia by more completely circumscribed calices, wall thinner, no 



ridges between valleys *P. calicifera Gardiner. 8 



Corallum an attached lamina, without hydnophoroid protuberances. 



Corallum an expanded, thin lamina, attached by a large area; upper surface subgibbous; calices 

 3 or 4 mm. in diameter. Some calices may be in series, separated by gently convex 



ambulacra. Columella a rather well-developed tubercle P. explanulata Lamarck. 



Corallum an expanded, thin lamella which appears to be incrusting; upper surface flat or slightly 



gibbous; calices 2.5 to 3 mm. in diameter; columella rudimentary or absent. .P. diffluens Lamarck. 

 Corallum attached by the middle, forming a moderately thin and expanded lamella; upper 

 surface slightly gibbous, rarely showing slightly elevated lines; calices in obscurely 

 concentric lines; 5 mm. in diameter; columella rudimentary, papillary (fossil, 

 Egypt) P ehrenbergi (M. Edw. and H).' 



'Ortmann has described from Ceylon a coral under the name Tichoseris angulosa, which seems to belong in the 

 divaricata group of Pavona. See Zool. Jahrb., Abtheil. fur Syst., vol. 4, 1889, p. 515, pi. 14, fig. 1. 



'These three supposed species are probably synonyms of P. explanulata Lam. 



'Synonyms of P. varians Verrill. 



'Von Marenzeller describes in Mitth. Naturhist. Mus. Wien, vol. 18, p. 126, fig. 4, rooi, a specimen referred by 

 him to this species. He expressed the opinion that the species belongs to the genus Coscinarcea and not to Pavona. 



