l8o PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



plates the diameter is usually less, between slightly less than I mm. and 1.5 mm., 

 and the coiallites are crowded. The usual diameter of well-developed radial 

 corallites in A. plicata is nearly 2 mm., but the diameter of some corallites is only 

 I mm. The shapes of the plates are very similar in both, but as A. cuneata has 

 more spreading, more crowded, and smaller radial corallites than A. plicata, it has 

 a decidedly different appearance. 



These are three closely related species, and possibly larger collections may 

 result in combining A. plicata with A. cuneata, but, according to the material at 

 present before me, all are distinct. 



Stations, Murray Island. — Southeast reef, line I: 



1,400 feet from shore; depth 14 inches; bottom hard, rocky. 

 1,600 feet from shore; depth 10 inches; bottom hard, rocky. 



Distribution. — ^Tongatabu (Brook, type); Rocky Island, Great Barrier Reef 

 (Brook); Murray Island, Torres Strait. 



Acropora (Conocyathus) polymorpha (Brook). 

 Plate 81, figures I, 2, 3, 4, 5, specimens from Fanning Island. 



1846. Madrefora abrotanoides Dana, U. S. Expl. Exped., Zooph., p. 477, plate 41, fig. i (non Lamarck). 

 1893. Madrepora polymorphra Brook, Cat. Genus Madrepora, p. 169, plate 31, figs. B to D. 



A fine suite of this species was collected at Fanning Island by Dr. Fred Baker 

 and Mr. C. Elschner. Brook's description is excellent and is quoted in full. 



"Corallum fruticose, spreading ramose; branches 8 to 20 cm. long, usually about 

 1.5 to 2 cm. thick, gradually tapering; the branches bear numerous branchlets, spreading 

 usually at an angle of 80° to 90°, and varying in importance from thickened and elongate 

 proliferous corallites to subterete and tapering twigs 4 cm. long and i cm. thick. Axial 

 corallites 1.5 to 2 mm. diameter and 0.5 to 2 mm. exseit, wall thick or comparatively thin. 

 Radial corallites compressed nariform or tubo-nariform, unequal, the longer ones becoming 

 tubular and proliferous. Some distance below the apex all become verruciform with a 

 dilated wall, which gradually becomes reduced to a ring-shaped fold. Immersed corallites 

 are usually wanting even in the older parts of the colony, but in one or two specimens, which 

 agree closely in other respects, immersed corallites may take the place of those with a ring- 

 shaped lip. Radial corallites 1.5 mm. diameter or under, and i-S to 3 mm. or more in length; 

 aperture oval, wall varying in thickness in different specimens; always thickened some 

 distance below the apex of a branch, and in some cases quite to the apex; in the latter case 

 the wall of the axial corallites is also thickened. The axial corallites are provided with 

 12 septa, none of which are very prominent; those of the radial corallites are also usually 

 narrow, including the directives; in the corallites situated some distance from the apex 

 the second cycle is almost as well developed as the first. Corallum dense, even near the 

 apex of a branch in most specimens; surface and wall finely and closely echinulate. 



"The species which Dana referred to M. abrotanoides is quite distinct from the type 

 of Lamarck, with which the description given by M. Edwards agrees closely. The descrip- 

 tion and figure of Dana agree very well with the species here described and I have therefore 

 placed the name as a synonym. It is possible that more recent authors may have taken 

 Dana's species for the true M. abrotanoides, and the synonymy is thus uncertain at present. 



"There is considerable variation in this species, both in the branching and in the thick- 

 ness of the corallite-wall. The specimens which have come under my notice fall more or 

 less completely into three groups: 



"a. Branches elongate; corallite-wall thin or onl)^ slightly thickened near the apex of a 

 branch, but becoming considerably thickened below. A few immersed corallites 

 may or may not occur near the base of the branches. 



"b. Branches shorter and more subdivided; corallites often 2.5 mm. diameter, all with 

 thick wall and rounded lip. No immersed corallites. 



"c. Branches thick and stunted, with short branchlets. Immersed corallites extend- 

 ing between the bases of the branchlets to near the apex. 



"Indo- Pacific Ocean; Malacca; ?Fiji." 



