POLYZOA FROM THE SILURIAN FORMATION. 267 



I have seen one specimen, in the collection of Mr. Dyer, of Cincinnati, 

 in which the spaces between th'e cells are very minutely porous or tubu- 

 lar, and I am informed by Mr. James that a similar specimen exists in 

 his cabinet. It is possible these may constitute a distinct species. 



Position and locality : Cincinnati group, Cincinnati, Ohio. 



Alecto auloporoides, Nicholson. 



Plate 25, figs. 2, 26. 



Polyzoary creeping, adnate, of narrow branches, which divide at more 

 or less acute angles, and repeatedly inosculate, so as to give rise to a 

 complicated network, the meshes of which are usually more or less ellip- 

 tical, and have a long diameter of one line, less or more. Cells tubular, 

 partially immersed, but free close to their apertures, sometimes uniserial, 

 but more commonly arranged in two alternating rows, and sometimes 

 irregularly disposed at the points of anastomosis of the branches. About 

 six or seven cells in the space of one line. Cell apertures terminal, cir- 

 cular, of the same diameter as the tube, the last portion of the cell being 

 more or less conspicuously elevated above the general surface. 



This form seems to have been usually regarded as identical with 

 Aulopora arachnoidea, Hall, to which it bears a considerable superficial 

 resemblance ; but it is certainly distinct, and it seems to me to be an un- 

 equivocal Alecto. It is nearly allied to A. frondosa, James, from which it 

 is distinguished mainly by its much more slender habit and graceful 

 form, and by its generally having its cells arranged in a single or double 

 series. 



Podtion and locaZity : Cincinn&ti group, Cincinnati, growing upon Stropkomena alter- 

 nata, Conrad. Collected by Prof. Edward Orton and Mr. U. P. James. 



Alecto confusa, Mcholson. 



Plate 25, fig. 6. 



Polyzoary adnate, forming thin crusts, which envelop foreign bodies. 

 Cells tubular, multiserial, arranged in irregular transverse rows, im- 

 mersed towards their bases, free and elevated above the surface towards 

 their mouths. Cell apertures circular, terminal, of the same diameter 

 as the tube, about five in the space of one line. 



All the examples of this species that I have seen are parasitic on the 



