MIAGARA GHOUP. 



163 



Genus HORNERA (Lamouroux). 



This genus was established by Lamoroux, for some species of Zoophytes, which by La- 

 marck were left united with Retepora, and which differ from them in being arborescent, and 

 do not form a network, while their ramifications are sometimes large and also slightly anasto- 

 mosed ; above all, however, they differ in having the cellules salient, almost tubulous or 

 alveolar, and united in fascicles. 



The following species is placed under Hornera, simply from having the round tubulous 

 cells. The description of the genus would include all arborescent or ramose forms like Retepora 

 that do not form a network ; and therefore the R. diffusa, described above, would fall under 

 this genus. I have preferred to leave this under Retepora, chiefly from the form of the cells. 

 Fmlher investigation will probably render it necessary to separate the ramose non-reticulate 

 forms with angular cells, from true Retepora ; and those with round or tubular cells may 

 fall under Hornera, or more probably constitute a distinct genus. 



557. 1. H0RNERA1 DICHOTOMA (n. sp.). 



PL. XL C. Fig. 3a- d. 



Stems minute, semicylindrical, rigidly branching or bifurcating ; one surface striated longi- 

 tudinally, the other celluliferous ; cells with round or oval apertures, which open from the 

 summit of a pustuliform elevation. 



This species is extremely minute, its characters being scarcely distinguishable with the naked 

 eye. In its striated and poriferous surface it resembles in general characters Retepora ; but 

 the mode of branching is different, and the cells are round or oval, with the openings elevated 

 above the surface of the branch, which does not occur in Retepora. 



Fig. 3 a, b. A bifurcating fragment, natural size, and a part of the surface enlarged, showing 



the form and arrangement of cells. 

 Fig. 3 c, d. The striated or non-celluliferous surface, natural size and enlarged. 



Position and locality. This coral occurs on the surface of thin calcareous layers in the shale 

 at Lockport and Rochester. 



