1882.] MR. S. O. RIDLEY ON THE CORALLIID^. 221 



Atlantic. The AmphihelicB are found in the North Atlantic and 

 Florida seas, besides off Madeira ; but Cladocora debilis appears to 

 be a local species. The Balanophyllia is new, and has no definite 

 alliances. Ceratotrochus johnsoni is a remarkable form of a genus 

 of very great distribution ; and Caryophyllia endothecata is so im- 

 portant a coral that I shall venture to write a separate memoir 

 about its bearings on classification. 



EXPLANATION OP PLATE VHI. 



Fig. 1. Caryophyllia endothecata, p. 216, natural size. 



2. , the calice, magnified, 



3. , interseptal lociili, magnified. 



4. , eostEe, magnified. 



5. Ceratotrochus johnsoni, p. 217, natural size. 



6. , a second specimen, natural size. 



7. , the calice, magnified. 



8. , the costffi, magnified. 



9. Balanophyllia brevis, p. 219, natural size. 



10. , magnified. 



ll. , calice, magnified. 



12. , diagram of the septal arrangement. 



On the Arrangement of the Coralliidce, with Descriptions 

 of new or rare Species. By Stuart O. Ridley, M.A.^ 

 F.L.S., &c., Assistant in the Zoological Department, 

 British Museum. (Communicated by Dr. Gtunther, 

 V.P.Z.S.) 



[Eeceived January 23, 1882.] 

 (Plate IX.) 



The small group of species which has been thought worthy of 

 separation from the rest of its Alcyonarian allies as a distinct family 

 under the name Corallidce (more correctly Coralliida), is chiefly 

 remarkable in its structural characters for possessing a continuous 

 stony axis, covered by only a thin cortical layer of a softer spicuH- 

 ferous material, into which the polypes are retractile. Its best claim 

 to general notice lies in the fact that the Precious Coral of commerce 

 {Corallium ruhrum, Costa, rectius nohile, Pallas) is one of the only 

 three species hitherto known to exist in the seas of the present time 

 which have been included in it. The other two species are scarcely 

 known, even to students of the group. Thus but one specimen of the 

 species described by Dana (U. S. Expl. Exped., vol. vii. p. 64 1, pi. Ix. 

 fig. 1) under the name of Corallium secundum seems to have ever 

 been described ; and but one specimen of the third species, described 

 by the late Dr. Gray (P. Z. S. 1860, p. 393, Rad. pl. xviii.) under 

 the name of Corallium (subsequently altered to Hemicorallium) 

 johnsoni, was obtained in the first instance, and I know of no other 

 authentic specimen. The original specimen of this species, how- 

 ever, IS fortunately preserved in the national collection; that of 



