CAMPTOSTROMA, A LOWER CAMBRIAN FLOATING 

 HYDROZOAN 



By Rudolf Ruedemann 



State Paleontologist, New York State Museum, Albany, N. Y. 



A problematic fossil from the Lower Cambrian of Pennsylvania, 

 belonging to the United States National Museum, has been submitted 

 to me for study and description. The material consists of molds 

 only, one specimen showing impressions of the two opposite sides, 

 two others impressions of one side. The incompleteness of the pres- 

 ervation would at first sight discourage a study of the form, but its 

 great age and perplexing appearance invite examination, and the 

 sharpness of the casts permits some fairly conclusive determinations. 



The outline of the fossil is broadly elliptic to subcircular, the 

 supposed upper surface slightly convex with a shallow central de- 

 pression, the supposed under surface flat or slightly concave. The 

 organism was originally either disklike or lenticular — perhaps even 

 a spherical body, the degree of post-mortem compression not being 

 determinable in the fossil state. It is probable that the body was 

 biconvex and relatively soft, as the oblique compression has made 

 a concentric semicircular fold on what I consider the upper surface, 

 with a corresponding ridge on the underside. (See fig. 1.) 



No trace of the original substance of the organism is preserved, 

 but a limonite film in the holotype and a silica film in another speci- 

 men, between the matrix and the mold of the fossil, suggest the 

 presence of a periderm. Tlie sharp impressions of both upper and 

 under surfaces leave no doubt of the substantial character of the 

 walls and indicate the presence of a surficial skeleton composed of 

 loosely connected spicules, forming the coenenchym. The spicules 

 may have been chitinous in substance, or they may have contained 

 some lime, the form then being comparable to some recent Alcy- 

 onacea, as the Xenidae, the spicules of which also contain but a 

 relatively small proportion of lime, or to the Alcyoniidae, in whose 

 soft, fleshy colonies the spicules are not fused. 



The fossil suggests at first sight an echinoderm, but the absence 

 of a distinctly plated integument and of mouth and anus is adverse 

 to that view. Neither can a reference to the sponges, which might 

 be suggested by the composition of the body wall of spicules and the 

 presence of numerous openings (possibly inhalant pores), be upheld. 



No. 2954.— Proceedings U. S. National Museum, Vol. 82, Art. 13 



150263—33 1 



