ARMSTRONGIA, A NEW GENUS OF DEVONIAN GLASS 



SPONGER 



BY JOHN M. CLARKE 



In recently discussingthe Devonian glass sponges, I described under 

 the name of Ceratodictya oryx (N. Y. State Mus. 

 Bui. 196, p. 180, pi. 2, 1918) a slim and strongly annulated form, 

 expressing at the time some hesitation in referring these short and 

 simple twigs to the genus Ceratodictya which had been created 

 some twenty years ago ^for the reception of much larger and more 

 regularly developed reticula. Our knowledge of this sponge has 

 been enlarged in a very interesting way through the acquisition of 

 a slab of Chemung sandstone recently taken from the original local- 

 ity of the species, on the broad surface of which apparently two in- 

 dividuals of the sponge are laid out in impression, in what would 

 seem to be approximately complete extent. Whilet he structure 

 of the branches indicate its specific identity with C. oryx, its 

 extraordinary branching form and accessory structures show that 

 this sponge has nothing to do generally with Ceratodictya. 



In the figure here presented of this slab the relief is given rather 

 than the natural impression, the picture being made from a cast of 

 the original. It will be seen that we have here to deal with a diffusely- 

 branched sponge whose form and direction of branching is approxi- 

 mately determinable from the form of the annulations. These have 

 a normal expression of ensheathing rings with their steeper slopes 

 directed backward or toward the root. This index is not easy to 

 follow in all parts as occasionally the annulations show little differ- 

 ence in upper and lower curves. On this slab there seems to be more 

 than one colony represented, possibly three in all; but one is con- 

 spicuously shown, displays the form of structure at the joints and 

 indicates that branching is very diffuse. The surface of these annu- 

 lated branches shows fine striations on the sandstone matrix in the 

 interannular spaces, but little can be seen of spicular tufts projecting 

 from the annuli. 



Other structures are indicated: Several of the branches show 

 terminal sheaths or smooth conical extensions running out into a 

 blunt tnmcated apex. Two or three of these are in place and several 



^Hall and Clarke, Dictyospongidae, p.117 (N. Y. State Mus. Mem. 2, i 



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