ART. 13 A NEW LOWER CAMBRIAN HYDROZOAN RUEDEMANN 6 



zooidal tubes with an interior reticulate columella, finds its closest 

 homology in the Tubulariae, such as the genera StoliczhaTia and 

 Heterastridium from the Triassic of Europe and Asia. In a some- 

 what less degree they resemble the Paleozoic Stromatoporoidea. 

 which are currently placed with the Hydrocorallinae and Tubulariae 

 as an early aberrant order, and which are able to form colonial 

 stocks and possess surfaces similar to those of GamptostroTna. 



From both the Hydrocorallinae and Stromatoporoidea this form 

 is separated by its obvious lack of a strongly calcareous coenenchym, 

 although it is quite possible that the zooids of G amptostrOTiia had a 

 chitinous periderm and a chitinous, or onlj'' slightly calcified, basal 

 coenenchym, as in many recent Tubulariae. The presence of the 

 limonite film in the holotype and of the siliceous film in another 

 specimen between the matrix and the impression of the fossil makes 

 it probable that the polyp stocks were protected by a chitinous outer 

 layer (periderm) as in many recent Tubulariae, and the mold we 

 see is that of the chitinous or slightly calcareous skeleton secreted at 

 the base of the outer layer of zooids or polyps. 



From the sharp preservation of the surface features (of the 

 last coenenchym), loss of all interior structure, and the clear evidence 

 of a considerable flexibility and compressibility of the body, I am 

 led to the conclusion that this organism had a chitinous skeleton and 

 resembled most of the present Tubulariae. It may well have been 

 the ancestor of the Stromatoporoidea, which later developed much 

 greater expansion of the coral stocks, which necessitated protection 

 and support by deposition of lime in the skeleton. 



As the colonial stock was lenticular if not subspherical, and there 

 is evidence of the presence of only one layer of coenenchym under- 

 lying the youngest generation of zooids, it is possible that the earlier 

 and deeper layers of the coenenchym were not preserved, owing to a 

 lack or small percentage of chitin and lime; or it is possible that 

 they were dissolved on further growth and the interior then filled 

 partly with gas (perhaps contained in the mesogloea) and the entire 

 hydrosome was floating. This is by no means improbable for the 

 following reasons : There are floating pelagic colonial stocks or hydro- 

 somes of hydrozoans to-day, as in the family Pelagohydridae and 

 three species of the genus Margelofds (see Hickson, 1909, p. 274). 

 The presence of hydropores on both the upper and under sides of 

 the colonial stock indicates freedom for the zooids to expand on all 

 sides, or a free floating condition of the hydrosome, while the light- 

 ness and imperfect development of the skeleton point in the same 

 direction. Finally, there is little doubt among biologists that the 

 mobile habit preceded the sessile and the discovery of the ocean 

 bottom. In the case of this colonial stock, budding would then 



