214 Christmas Island. 



done so on the character of the columella. But in the ij])Q 

 species of Coeloria the columella is quite well developed (see e.g. 

 the original figure of Ellis k Solander, Hist. Zooph., pi. xlvi, 

 figs. 1, 2); it is in fact better developed than in some species 

 of Mceandriiia. 



The distinction based on the columella appears to me insufficient 

 for the separation of the two genera. The length of the confluent 

 calicinal series may, however, yield an adequate basis ; for those 

 corals in which the calicinal series are very long may be con- 

 venientlj^ kept distinct from those in which the calicinal series 

 are short and independent calices predominate. Cceloria, with 

 C. dmlalea as the type, would include the latter group. The naming 

 of the former group is a difficult question. The most convenient 

 name would be Mceandrina, but that name would have to be 

 designated as Ed. & H., 1848, non Lamarck, 1801. For according 

 to the original foundation of that genus its type is Mmandrina 

 peetinata, Lam., which most authors have taken as the type of the 

 genus Pectinia. 



Whether the inconvenience of the change in the name 

 M(Bandrina, which observance of the laws of nomenclature would 

 involve, be too serious for obedience to the law to be advisable, 

 I leave zoologists to settle, and so provisionally retain it. 



Gcniastraea retiformis (Lamarck), 1816. 



Astrcca retiformis, Lamardv, 1816. Hist. nat. Anim. s. Vert., vol. ii, p. 265. 

 Goniastrcea retiformis, Edwards & Haime, 1849. Mem. Astr., pt. iii : Ann> 



Sei. nat., ZooL, ser. iii, vol. xii, p. 161. 



This species is represented at Christmas Island by a recent 

 specimen determined by Mr. Bernard and several fossil specimens. 

 The latter show the following characters : — The corallites are fi'om 

 3-4 mm. in dia. ; the walls are from '5 mm. to something under 

 1 mm. in thickness ; the septa belong to three cycles, of which the 

 third is incomplete ; the columella is loose and sometimes hollow ; 

 the pali are indistinct ; the corallites are elliptical, quadi'angular, 

 pentagonal, or hexagonal in shape. 



The corals agree closely with G. capttata, Stud.,' which, as 

 Ortmann'^ suggests, is probably a variety of G. retiformis with 

 thinner walls, somewhat exsert septa, and more open calices. The 

 recent specimen from Christmas Island resembles the capitata form,, 

 the characters of which are not preserved in any of the fossils. 



Distrihiition. — Christmas Island. 

 Eecent : 



Fringing Reef, Flying Fish Cove. 



1 Th. Stiider, Beitr. Fauna Steinkor. Singapore: Mitth. Naturf. Gesell. 

 Bern., 1880 (1881), pp. 40, 41, fig. 8. 



2 Ortmann : op. cit., p. 173. 



