DESCRIPTIONS 



OF THE SPECIES OF FOSSIL KETICULATE SPONGES, 

 CONSTITUTING THE FAMILY DICTYOSPONGID^E. 



By James Hall. 



In 1882 the writer communicated to the American Association for 

 the Advancement of Science, at its meeting in Montreal, some " Notes 

 on the Family Dictyospongidae," accompanied by lithographed plates 

 from the 35th Eeport on the State Museum of Natural History, illus- 

 trating the genera cyathophycus, dictyophyton, phragmodictya, 

 clathrospo:n"GIA, PHYSOSPONGiA, and showing their relations to 

 uphakt^kia. The paper was not communicated for publication ; but 

 an abstract, together with the plates and explanations, " subject to re- 

 vision," was placed in the hands of the secretary for preservation, 



The delay in printing the Museum Report has afforded an oppor- 

 tunity of acquiring material for a farther study and review of the 

 characters and relations of the forms indicated in the original title. 

 Several new species have been added, and some additional knowledge 

 has been obtained regarding their habit of growth and mode of oc- 

 currence. 



On account of the continued delay it has been deemed advisable to 

 present the following abstract from the memoir on these fossils as 

 already prepared for publication. 



The structure of the frond, which characterizes every member of 

 this family, may be described as a reticulation of tubular spicules, 

 forming rectangular meshes. In the simpler forms these meshes 

 alternate in size and strength, owing to the regular alternation in the 

 size of the bundles of spicules, which determine the meshes. In the 

 prismatic and nodose forms, certain bundles of spicules become very 

 much developed, and produce the charactisticform and ornamentation 

 of the cup. The middle layer is uniformly reticulate ; while the 

 inner and superficial layers show an oblique and sometimes a radiate 

 arrangement of spicules. In the highly ornamented species, the out- 

 side layer of spicules is often produced into tufts, spines, and intersecting 

 fimbria or laminae, of greater or less prominence. 

 [Sen. Doc. No. 38.] 59 



