Z PROCEEDINGS OF THE NATIONAL, MUSEUM vol.82 



There is nothing to indicate the presence of an ostium, and such 

 organs as the monticules also distinguish it from the sponges. Like- 

 wise the possibility that this peculiar form might be referable to the 

 Receptaculidae, now considered by some as calcareous algae, is not 

 supported, as the fossil lacks the regular surficial pavement of quin- 

 cuncial elements so characteristic of those problematical organisms. 



All the features of the fossil considered, a reference to the hydro- 

 zoans appears most apt. The strange Paroysoneina, cryptophya 

 Clarke from the Naples beds of New York is at once suggested, 

 having in common with our fossil the general outline, possible disk- 

 like shape, and concentric ring of radial ribs. Paropsoneina is now 

 considered as the float or pneumatophore of a large hydrozoan, 

 which in structure resembles the float of Porpita. (See Ruedemann, 

 1916, p. 22.) Another similar fossil is the Ordovician Discophyllwn 

 peltatum Walcott, considered as a medusa by Walcott but also re- 

 ferred by Ruedemann {ibid.) to the Hydrozoa as a probable float of 

 Siphonophora. Both Paropsonema and Discophyllum, while strik- 

 ingly similar to Camptostroma in general features, possess charac- 

 ters that unite them with Porpita but that are not found in Camp- 

 tostroma. Paropsonema shows distinct cycles of air chambers and 

 concentric lines, while Camptostroma, in the cancellated skeleton and 

 the monticules, possesses characters that are not found, to my knowl- 

 edge, in any floats of siphonophores but that point distinctly to the 

 Tubulariae. 



The central portion of the disklike body on one (upper?) side is 

 marked with numerous large subcircular depressions sunk into a 

 granular surface from which, in some places, faint radiating de- 

 pressed lines extend, suggesting the astrorhizae of the stromatopo- 

 roids. The granular surface in one specimen results from small, 

 closely packed spicules. This area is surrounded by a ring of sharp 

 folds or ribs, the spicules of which are coarser and less closely packed 

 than in the central portion, leaving numerous pores between. These 

 spicules are intermediate between those of the upper central area, 

 the marginal area, and the underside. The ribs fade into the mar- 

 ginal portion and underside, both of which are characterized by a 

 polygonal network of small, widely spaced, vertical, platelike spic- 

 ules. As a result of this plate arrangement the whole looks like 

 the vermicular, perforate sclerenchyma of numerous stromatoporoids 

 or more recent Hydrocorallinae. In some areas a pavement of short 

 pillarlike spicules appears. The underside is characterized by num- 

 erous monticules with depressed centers showing groups of small 

 circular pits and nodes surrounded by radiating trabeculae or 

 tubes (?). 



The general form of the bodies, as well as the structure of the 

 cancellated surface of the coenosarc and the monticules, suggesting 



