MADEEPORA. 67 



frequently become confluent, and are echinulate or rough ; this is precisely the condition 

 described by Khmzinger. The description of Klunzinger, however, differs in several points 

 from that given above, and as it probably represents more nearly the normal characters of the 

 species, the following particulars are appended : — 



Corallum arborescent, with long terete, spreading, and acuminate branches, which bear 

 numerous rudimentary and spreading proliferations. Axial corallites 2 to 2'5 mm. broad and 



2 mm. exsert, costulate, scarcely broader than the radial corallites ; these are rather distant, 

 short, wide nariform or subtubular with the inner part of the wall wanting, 2 to 3 mm. broad 

 and 1 to 3 (rarely 3) mm. long, aperture about 1 mm. A number of short tubular proliferous 

 corallites occur at intervals, which indicate new outgrowths. On the under surface of the 

 branches the wall of the corallites is extremely short, but rarely absent altogether. Corallum 

 rather porous in section ; surface strongly ribbed, the ribs spinose and often confluent, with 

 spaces between. 



Indian Ocean : Red Sea, Seychelles. 



a, h. Seychelles, 4 to 12 fathoms. H.M.S. ' Alert.' 82. 10. 17. 159 & 146. 



49. Madrepora borealis. 



Madrepora borealis, M.-Edwards & Haimo, Coralliaires, t. iii. p. 144. 



Corallum closely resembling that of M. arabica in habit and density. The type specimen 

 consists of a terminal fragment 8'5 cm. long; diameter of main branch 1'4 cm. Lateral 

 branches numerous, up to 1 cm. in diameter and 5 cm. long, each bearing 2 or 3 proliferous 

 branchlets on the anterior surface ; posterior surface mostly void of branchlets and with fewer, 

 shorter, and often smaller corallites. Axial corallites probably 2'5 to 3 mm. diameter, little 

 over 1 mm. exsert, with thin wall and deep cup; septa in two cycles, both moderately 

 developed, the directives only slightly broader than the other primaries. Radial corallites 

 chiefly very short tubular below, 1"5 to 2 mm. diameter, scarcely projecting; the upper ones 



3 to 4 mm. long, appressed tubular, with recurved lip, often 2 to 2'5 mm. in diameter, 

 Corallum porous ; surface clothed with longitudinal spinose plates connected by a network ; 

 wall broadly striate and echinulate, fragile. Septa of the radial corallites in two moderately 

 developed cycles, directives broad. 



In spite of the presence of a second cycle of septa, I have felt it necessary to associate 

 this species with M. arabica on account of its extremely close resemblance in other respects. 

 I have, indeed, doubts as to whether it is really distinct. In M. borealis the corallum is more 

 porous than in the type specimen of M. arabica, the corallites have usually a greater dia- 

 meter; the prominent ones are more numerous, and the septa are much better developed. In 

 M. spinulosa, Klunz., which I regard as a synonym of M. arabica, the corallum is porous and 

 the prominent corallites are larger (?) and more numerous. 



Some mistake has evidently been made in the habitat of the type of this species ; it is 

 almost incredible that a species of the genus Madrepora should be found in Arctic Seas. 



[White Sea, near Archangel.] 



