MADEEPOEA. 41 



plates; wall costulate, the costse divided into dentate plates below. Axial corallites 

 prominent, ?2'5 mm. diameter; radial corallites short, tubular, mostly 1-5 to l? mm. long 

 and 1 mm. diameter, with a thin wall and circular aperture ; a few smaller ones are scattered 

 amongst the others, but none are immersed; most are placed at an angle of about 45°, and 

 are therefore not so spreading as in M. formosa, Dana. One of the fragments from 

 Amboina, referred by Quelch to M. gracilis, appears to me to belong here. Some of the 

 specimens from Tahiti and Tongatabu are bushy, with proliferous twigs near the apex. 



Pacific Ocean : New Hanover, Fiji, Tahiti, Amboina, Tongatabu. 



a. 



Tahiti. H.M.S. ' Challenger.' 86. 12. 9. 236. 



b. Tahiti. H.M.S. ' Challenger.' 86. 12. 9. 237. 



.80. 11. 25. 235. 

 c-e. Papeete Reefs, Tahiti. H.M.S. ' Challenger.- 



r»U. il. 25. 235 

 .'4 86. 12.9.406. 

 (91. 9. 9. 2. 



/.Amboina. H.M.S. 'Challenger.' 86.12.9.229. {= M. gracilis, 



Quelch, part.) 



? 93. 4. 7. 74 & 76. 



? 93. 4. 7. 75 & 77. 



J. J. Lister, Esq. [P.] . 91. 3. 6. 4. 



D. Prominent corallites short, erect, tubular, unless near the apex of a branch. 



a. Branches 2 cm. thick or more. 



18. Madrepora tylostoma. 



Heteropora tylostoma, Ehrcnberg, Corallenth. d. roth. Meeres, p. 111. 

 Madrepora tylostoma, Dana, Zoophytes, p. 489. 



The type specimens are much worn, and belong to a stout and laxly-arborescent species 

 resembling M. secunda or M. muricata var. cervicornis in habit. Stoutest branches 2*5 cm. 

 thick ; in one or two specimens they are fused together with large spaces between, measuring 

 10 by 5 cm. The axial corallites are not preserved. The radial corallites are rather distant, 

 spreading at right angles ; very short tubular with an oblique aperture ; some are sub- 

 immersed and smaller ; they vary from to 2 mm. in length, but most do not exceed 1 ram., 

 diameter 1 to 1'5 mm. One cycle of septa is moderately developed, and a second is present 

 in rudiment. Corallum dense, not reticulate in section; surface rather dense, reticulate, 

 with blunt echinulations ; wall striate. 



Another specimen in the Berlin Museum, from Mauritius {Mobius), differs from the 

 types only in the sometimes less-oblique aperture of the radial corallites. Branches \o cm. 

 diameter and under. Axial corallites 2 to 2"5 mm. diameter, 2 mm. exsert. Surface and 

 wall strongly spinose. 



Indian Ocean : Mauritius {Berlin Museum). 



