124 Dr. II. A. Nicliolson on Species 



in the form and mode of growth of the cells, and in the posi- 

 tion of the cell-mouths. It is very readily distinguished from 

 the following forms by the fact that the cells are not at all 

 immersed, by the fact that each cell springs directly from 

 another, by the cells being strictly uniserial, and by the posi- 

 tion of the cell-mouth on the front face of the swollen cell. 

 The cells arc distinctly pyriform in shape, attenuated below, 

 with a smooth surface, the aperture being orbicular or oval 

 and destitute of notches or spines. The network formed by 

 the polyzoary is usually a very close one, the branches being 

 given otf from the sides of the cells, usually at intervals of 

 from half a line to two thirds of a line. 



All the examples of this species which I have seen are 

 parasitic upon IStropliomena alternata, Conrad. Hall's speci- 

 mens are from the Trenton Limestone ; but there can be no 

 question as to their identity with ours. 



Locality and Formation. — Abundant in the Cincinnati 

 Group (Hudson-River Formation) near Cincinnati, Ohio. 



2. AJecto auloporoidesj Nicholson. PI. XI. figs. 2-2 h. 



Polyzoary creeping, adnate, of naiTOw branches, which divide 

 at various angles and repeatedly inosculate, so as to give rise 

 to a complicated network, the meshes of which are more or 

 less elliptical, and have a long diameter of one line more or 

 less. The branches vary in width from one fifth to one third 

 of a line. Cells tubular, partially immersed, free towards 

 their apertures, sometimes uniserial, more commonly arranged 

 in two alternating rows, sometimes irregularly disposed at the 

 points of anastomosis of the branches ; from five to six cells 

 in the space of one line in the narrower branches. Cell- 

 apertures temiinal, circular, of the same diameter as the tube, 

 the last portion of the cell being more or less conspicuously 

 developed above the general surface. Surface apparently 

 smooth. 



The Ohio palaeontologists appear to regard this as being 

 the Aulopara arachnoidea of Hall; and, indeed, it seems 

 probable that Hall included this under liis s])ecies. This, 

 however, is an undoubted ^ /ecto ; and I think the name of 

 Aulopora arachnoidea ought to be restricted to the form which 

 I shall shortly describe under this name — a form which is 

 very similar in general appearance to Alecto aidojyoroides^ and 

 occurs -with it in the same beds, but which seems certainly to 

 be an Aulopora^ and is at any rate specifically distinct from 

 the present fossil. 



Alecto auloporoides is very nearly allied to A. frondoaa^ 



