78 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 14, 



Madrepor(B and Astroites of preceding authorities ; but the then* 

 state of knowledge necessarily occasioned a want of definiteness of 

 leading characters. He nevertheless limited his genus to hemisphe- 

 rical and globular corals, with circular or subangular stars on the sur- 

 face ; but he did not assign any restriction to the number of lamellae ; 

 neither did he call attention to peculiarities of internal composition, 

 and their influence on external characters ; nor to the mode by which 

 young stars are developed. This want of precision, unavoidable forty 

 or thirty years ago, has gradually become an increasing source of 

 error, by being too closely adopted; and the evil assumes a still graver 

 aspect in extending the study from recent to extinct zoophytes, espe- 

 cially if the geological age of the fossil should be remote. Lamarck, 

 in his edition of 1816, gave only two extinct species, Ast. reticulata 

 and A. emarciata, corals possessing very opposite compositions ; but 

 M. De France t and Prof. Goldfuss J subsequently described a great 

 amount of additional species, without however any essential improve- 

 ment of the generic characters. M. de Blainville grouped in sub- 

 genera {pp. cit. p. 366 et seq.) the great mass of materials, recent 

 and fossil, of previous authorities, adopting for his basis chiefly the 

 form and relative position of the stars, slight advantage being also 

 taken of the nature of the lamellae ; but no allusion is made to struc- 

 tural combinations, or to the plan of producing young stellated cavi- 

 ties. " Plusieurs de ces groupes," says M. Milne-Edwards, " parais- 

 sent etre naturels et devront probablement, lorsqu'on connaitra la 

 structure des polypes qui y appartiennent, constituer des genres 

 distincts." (Lamk. ii. p. 404.) The groups however have not been 

 adopted even for existing corals, though they undoubtedly present an 

 onward arrangement ; and if palaeontologists, who can never hope to 

 see the living animal of the subjects of their research, had studied 

 M. de Blainville's subgenera with the aid of specimens and modern 

 discoveries, many anomalous determinations might have been avoided. 

 In Ehrenberg's Memoir on the Corals of the Red Sea (Beitriige, p. 95), 

 far greater precision is given to the genus AstrcBa, by limiting it to 

 those many-lamellated species which have the stellated cavities in 

 juxtaposition, and which produce young stars, within the area of a 

 specimen, by a fissiparous process ; while the species in which a simi- 

 lar mode of increase exists, but the stars have more or less clear in- 

 tervals between them, are placed in a distinct genus, Favia {op. cit. 

 p. 93) ; and those which develope new cavities between the pre- 

 existing are removed to another family. Mr. J. D. Dana, in his re- 

 cent work on Zoophytes §, arranges the corals referred by himself to 

 Astrcea in three subgenera : — 



* Astraea was established by Lamarck in the 1st Ed. of his Hist, des Anim. sans 

 Vert. pubHshed in 1801. The author of this notice cannot refer to it, but the 

 classification is given by De Blainville, op. cit. p. 35. The Seven-volume Edition 

 was commenced in 1816; and M. Milne-Edwards's edition, termed the second, in 

 1835. 



t Dictionnaire des Sciences Naturelles, tome xlii. 1826. 



t Petrefacta, &c.,vol. i. 1826-1833. 



§ Exploring Expedition, Zoophytes, pp. 200, 205, 184G. 



