410 Zoological Society. 



on one edge, and spiniferous or only with a slight tubercle on the oppo- 

 site one ; sometimes one edge has two spines and the other only one, 

 or a tubercle, and the extent of the truncation of the base differs in 

 every example. 



The same examination has also induced me to believe that the spe- 

 cimen which these authors have described under the name of Ptaco- 

 trochus Icevis, p. 283. t. 8. f. 15, is only a variety of the same species ; 

 and that Acanthocyathus Grayii, 293. t. 9. f. 2, is only a specimen of 

 the same species which has lost its compressed form. I have not 

 seen Rhizotrochus typus, p. 282. t. 8. f. IG, or Blastotrochus nutrix, 

 p. 284. t. 8. f. 14 ; but from the figures, I have great suspicions that 

 they are only modifications of the same species. 



To give some idea of the variations produced by local causes in 

 corals, I may state that the specimens which Messrs. JMilne-Edwards 

 and Haime have described under the generic name o^ Heterocyathus, 

 are only specimens of the genus Cyathus which have been changed 

 in form from their having grown attached to a spiral shell which was 

 inhabited by parasitic Crustacea. I have specimens showing all the 

 grades of change, from the nearly normal conical form of the genus 

 to the truncated form which has been described as the type of the 

 genus Heterocyathus. This form was well-described by Spengler in 

 * Nova Acta Ilafnise,' i. 240, and noticed by Gmelin under the name 

 of Madrepora Cochlea^ p. 3/63. 



Messrs. Milne-Edwards and Haime described two species of this 

 genus under the names of H. cequicostatusy t. 10. f. 8, and/Z^. Rous- 

 sceanus, t. 10. f. 9. Of the former he appears only to have seen a 

 single specimen. We have in the British Museum three very distinct 

 species, which may be thus described : — 



1. II. Cochlea = Mad. Cochlea^ Gmelin, S. N. H. cequicostatus, 



Milne-Edwards and Haime, 324. t. 10. f. 8. 



Coral subcylindric, hard, white, with narrow, equidistant, distinct 

 grooves, crenulated on the edges ; base rather dilated ; laminae nar- 

 row, sharp-edged, very unequal, grooved on each side, and with 

 crowded columns in the centre of the star. 



Hab. Chinese Seas. 



The holes on the outer surface are large and distinct. 



2. H. HEMISPHiERICA. 



Coral subcircular, depressed, subhemispherical, nearly flat below, 

 regularly convex above ; sides rounded ; plates of star broad-topped, 

 as if truncated, covered on top and sides with very numerous crowded 

 spines and tubercles ; centre of star roundish, with small columella. 



II ah, Chinese Seas. 



The plates of this species resemble those figured as belonging to 

 H. RoiisscBanus, I. c. 325. t. 10. f. 9 ; but the shape of all the two 

 specimens in the Museum, which are nearly similar, is quite distinct 

 from the view of the side of that species. 



3. H. EUPSAMMIDES. 



Coral polymorphous, base flat, sides shelving, sinuous, surface 

 covered with very close, irregular, sinuous, denticulated ridges, and 



