150 MONOGRAPH OF THE FOSSIL POLYZOA OF THE 



IIETERACTIS, (N. G.) G. and H. 



Colony discoidal, convex above, concave below ; beginning by one cellule, succeeded 

 by two, one placed exactly opposite the other. These continue to develope in a 

 straight line, but more rapidly in one direction than in the other, so as to form a straight 

 median line, from which the rest of the colony is developed, throwing the original 

 cellule far from the centre. New lines are developed at all angles from the first in a 

 radiating manner. Sometimes there is a second line formed by the bifurcation of the 

 first, at others it commences near what is to be the middle of the adult colony, and 

 occasionally it occurs that a new line is interpolated between these two. New lines 

 commence when arising from the median one, by a fully developed cellule, the inter- 

 polated lines sometimes commence by an abortive cellule. 



The cellules are always placed in straight lines ; the opening is large, and was un- 

 doubtedly close by a membrane in the living state. There is a vibracular opening 

 placed aside of each cellule, between the rows, exactly as in the true Lunulites. The 

 under sides of the colony is marked by lines corresponding with the lines of cellules 

 and is coarsely punctate but not perforate. 



"We place this genus provisionally in the FlustreUaridce of d'Orbigny for the same 

 reason that we have retained the genus Lunulites in the Escharidce. We propose, as 

 soon as we conveniently can, to examine the subject of the vibracular openings with a 

 view of ascertaining the value in relation to the classification of the Polyzoa, and hope 

 to be able before long to express a decided opinion on the subject. Time will not per- 

 mit us to do so at present. 



H. Duclosii, G. and II., fig. 39. — The only species. 



Lunulites id., Lea. Contributions to Geology, p. 110, pi. 6, fig. 203. 

 Colony slightly convex above, concave below, outline irregularly oval generally, 

 sometimes regularly elliptical. 



Cells arranged as described above. Form of the cells oval, variable, rounded in ad- 

 vance, straight on the proximal edge or encroached on by the preceding cell; anterior 

 and lateral edge somewhat elevated. Surface almost wholly occupied by the aperture, 

 which is of varied form, dependent on the form of the cellule ; normally it is ellipti- 

 cal, but this form is rather rare, it varies in every manner from that to subquadrate. 

 Between the rows of cellules is a depressed space, through which are pierced the vibra- 

 cular openings. These are sometimes elongate and rounded at the two extremities, 

 sometimes acuminate at one or both ends, and often constricted in the middle. 



The under side is characterized by very irregular lines, marking the backs of the 

 rows of cellules, and covered by a few large irregular pits. 

 From the Eocene of Claiborne, Ala. 

 The low convex form of the colony with its one or two median rows of cellules and 



