Each cell arises from the upper and back part of another, with the intervention of a short corneous tube which is prolonged from the interior of one cell to that of the one above.  The cell is furnished on each side at the top with a usually well-developed avicularium, in some species of huge size, and in some very minute, or entirely aborted.  This avicularian process in most cases supports above a hollow process, which is sometimes closed and more or less elongated, constituting a conical or acerose spine, sometimes open above and assuming the form of a shallow cup or receptacle.  In some species both modifications of this portion of the lateral process are met with in the same specimen.  This form of spine or cup—­as the case may be, is always distinctly separated by a septum from the cavity of the avicularium itself.  Below the avicularium there is also in many cases a third distinct cavity which is usually widely open, the opening being covered in very frequently by a convex transparent membrane, and its bottom apparently perforated by several minute foramina—­from this part of the lateral process there is in many species a prominent ala or keel prolonged to the bottom of the cell—­which ala not unfrequently divides into two branches, which, again coalescing at the bottom of the cell, circumscribe a more or less oval space, the bottom of which is also perforated by minute foramina or apparent foramina, and which is often covered over by a transparent convex membrane.  This membrane, however, as well as that which covers in the subavicularian space, is more usually broken off and wanting.

The inferior oval space above described is here termed the lateral area, and it is employed in the specific characters.  It would thus be correct to say—­that each cell is furnished with two lateral processes, each of which in the fully developed state consists of three distinct compartments—­one superior, a cup or spine:  a middle one, which is the avicularium:  and an inferior; and it would appear that one or more of these elementary compartments of the lateral process may be more developed than the next, or sometimes entirely aborted.  The mouth of the cell is situated at the upper part in front, and is of the same conformation as in the rest of the Cheilostomatous suborder.  An important generic character consists in the gemination of the cell at each bifurcation.*

(Footnote.  Table 1 figures 1 and 2.)

These characters are common to all the species included in the genus, which furthermore admits of being subdivided into two extremely natural sections or subgenera (or perhaps into three).  These subdivisions are named respectively the fenestratae, and the vittatae.