Speoiks ok thk Hamilton Group. 



65 



arms. There is, from analogy, probably no reason why these smooth and 

 ornate spicules may not have belonged to the same 8i)ecies, but the present 

 distmction will serve a useful purpose until more is learned of these fossils. 



SPECIES OF THE HAMILTON GROUP. 



DICTYOSPONGIA, gen. nov. 

 (For description see page 72.) 



DioTYOspoNGiA (?) Marcellia, Clarke (sp.). 



Plate xli, Figs. 8, 9. 



1894. 



Hyahstelia (?) Marcellia, Clarke. Thirteenth Ann. Rept. N. Y. State 

 Geologist, vol. 1, p. 177, pi. iv, figs. 19-22. 



The specimens upon which this species was based were found at the 

 horizon of the Marcellus shales, in the excavations made at the Livonia salt 

 shaft in Livingston county, N. Y.,* at a depth extending from 812 to 823 feet 

 from the surface. The fossils occur as broad, thin, film like expansions which, 

 being pyritized, make irregular splotches of 

 discoloration, tingeing the surface of the 

 black bituminous shales a yellowish or 

 greenish hue. Under enlargement these 

 patches are seen to be composed of masses 

 of rod-like and cruciform spicules. The 

 latter are hexactins ; many of them, which 

 exhibit four branches on the same plane, 

 show the abbreviated or nodifonn remnants 

 of the other two rising in the plane at right 

 angles ; in some, however, there seems to be 

 no evidence of more than four rays. With 

 these spicules are found, similarly pyritized, 

 lar^e and coai'se spicular bands, flat, straight, 



^ '■ I I a J FIOURKII. Major and minor stauractlnes ot Diclyo- 



thickened on the edges or in the middle, 'po^i/toyiforceuta, wim portion or iigaiat« «ptcuio. 



X 30. 



and similar in size and appearance to small 



blades of grass. These end abruptly at one end but taper to the other, though 



showing no evidence of terminating in any appliance for attachment. 



There is no evidence that these broad ribbon-like spicular bands 

 are composed of separate spicular rods ; on the contrary they are clearly 



* A detailed account of these excavationa and the succession of the faunas through a vertical section of 

 nearly fifteen hundred feet, is given in the worlt cited. 



