1 82 TABULATE CORALS. 



Genus Nyctopora, Nicholson. 



Gen. Char. — Corallum composite, massive, of polygonal 

 corallites, which radiate from the base of the spheroidal coral- 

 lum, to open on its upper surface, and are in complete contact 

 throughout their entire extent. Walls of the corallites thin, 

 and so completely amalgamated that no trace whatever of the 

 original lines of division between the tubes can be detected. 

 Mural pores numerous, small, in more than one series, occupy- 

 ing the sulci between the septa. Septa in the form of marg- 

 inal vertical ridges, which extend along the whole length of 

 the tubes, from ten to fifteen in number in each corallite, 

 not divisible into an alternating series of longer and shorter 

 lamellae. Tabulae numerous, complete, horizontal. 



Obs. — I have been obliged to establish this genus for the 

 reception of a coral from the Trenton Limestone of Canada, 

 which I have previously regarded as probably identical with 

 Columnaria Goldfussi, Bill. In its general form and aspect 

 this coral, in fact, is entirely similar to Columnaria Halli, mihi 

 (C alveolata, Bill.) ; and it does not differ in any superficially 

 obvious character from the typical species of Columnaria {C. 

 alveolata, Goldf, and C. calicina, Nich.), except in the marginal 

 and comparatively rudimentary condition of the septa. Thin 

 sections, however, place it beyond a doubt that the walls of the 

 present form are perforated by mural pores, and that the coral 

 in question must be placed in the Favositidcs. Whether or not 

 the walls of Columnaria (?) Halli are likewise perforate is a point 

 which at present I cannot determine, though I am inclined to 

 think that in this form also mural pores are present. If this 

 conjecture should be ultimately established, then this well- 

 known form (the Columnaria alveolata of American palaeon- 

 tologists) will also have to be removed to the genus now 

 under consideration. 



The corallum in the only certainly ascertained species of 

 Nydopoi'a is in the form of spheroidal or pyriform masses, 



