GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. 427 



This species in its typical form is generally present on the living 

 West Indian and Floridian reefs, and is usual in the Pleistocene 

 reefs of the same region. 



AGARICIA AGARICITES var. PURPUREA Le Sueur. 



1820. Agaricia purpurea Le Sueur, Mus. Hist. nat. Paris Mem., vol. 6, p. 276, 



pi. 15, figs. 3a, 36, 3c. 

 1902. Agaricia purpurea Verrill, Conn. Acad. Arts and Sci. Trans., vol. 11, 



p. 149, pi. 27, figs. 4, 4a, 46. 

 1902. Agaricia agaricites var. gibbosa Verrill, Conn. Acad. Arts and Sci. Trans., 



vol. 11, p. 148, pi. 27, figs. 1, la. 

 1912. Agaricia crassa Vaughan, Carnegie Inst. Washington Yearbook, No. 10, 



p. 153. 

 1912. Agaricia fragilis var. Vaughan, Carnegie Inst. Washington Yearbook No. 



10, pp. 153-154. 

 1915. Agaricia purpurea Vaughan, Washington Acad. Sci. Journ., vol. 5, p. 596. 

 1915. Agaricia purpurea Vaughan, Carnegie Inst. Washington Yearbook, No. 



14, p. 228. 



Locality and geologic occurrence. — Canal Zone, station Nos. 5849 

 and 6039 Pleistocene, Mount Hope, collected by D. F. MacDonald, 

 abundant. This variety is widespread on the living reefs in the 

 West Indies and Florida. 



Agaricia agaricites var. purpurea is one of the corals on which I 

 made many experiments at Tortugas, Florida. The following is an 

 account of one experiment: 1 



The result of one experiment with Agaricia gave unexpectedly important informa- 

 tion on the influence of environment on variation. On the piers of the Fort Jefferson 

 dock a thin, unifacial, subcircular, or reniform Agaricia, attached by the center of 

 the lower surfaces, is rather abundant. This seems to be a variety of Agaricia fragilis 

 (Dana). On the reefs off Loggerhead Key an Agaricia of massive form, several inches 

 in diameter and of somewhat less height, is abundant. This appears to be the same 

 as Agaricia crassa Verrill. One specimen of the thin Agaricia fragilis form attached 

 to a tile in June, 1910, had by June, 1911, assumed the Agaricia crassa growth-form. 

 This specimen was attached by its entire lower surface and seems to have had its 

 growth-form influenced by the wide basal attachment. It is evident that there is 

 here one species of Agaricia that under different conditions assumes different growth- 

 forms. In very quiet water it is thin, orbicular, or reniform, with a slight basal 

 attachment at its center, while on the reefs it is more strongly attached and has a 

 more massive growth-form. But, in the quiet waters, the massive growth-form may 

 be produced by giving the normally thin form a wide base of attachment, or there ia 

 a reaction to contact. On the reefs, when the water is strongly agitated, there is prob- 

 ably a clinging of the peripheral polyps to the basal support; this causes the basal 

 attachment to cover a larger area than in the more quiet waters ; then upward growth 

 from this wide base would produce the massive form. 



AGARICIA AGARICITES var. CRASSA Verrill. 



1902. Agaricia crassa Verrill, Conn. Acad. Arts and Sci. Trans., vol. 11, p. 145, 

 pi. 30, fig. 6; pi. 34, fig. 2. 



1915. Agaricia crassa Vaughan, Washington Acad. Sci. Journ., vol. 5. p. 596. 



1916. Agaricia crassa Vaughan, Carnegie Inst. Washington Yearbook, No. 14, 



p. 228. 



Carnegie Inst. Washington Yearbook No. 10, pp. 153-154, 1912. 



