72 DlCTYOSPONGID^. 



Heticvlum. The net work is very fine and sharp. The obscuration of the 

 fundamental prism-faces makes the prevailing meshes of small size, about 

 1.5 mm. on each side, and though these may be again divided, combinations of 

 them into larger quadrules are not emphasized. Thus the reticulation appears 

 very uniform throughout. 



Dimensions. The single specimen which has been observed of this 

 species, has a length of 170 mm. Its width at the base is 65 mm.; at the aper- 

 ture 75 mm.; on the median row of nodes, 60 mm.; across the median 

 constrictions, 42 mm. 



Locality. In the sandstone of the Portage group ; second falls of the 

 Tannery gully, Naples, N. Y, (Collected by D, D. Luther.) 



SPECIES OF THE CHEMUNG GROUP. 



DICTYOSPONGIA, gen. nov. 

 1855. Tetragonis, McCoy. British Palaeozoic Fossils, p. 62. 

 1880. Tetragonis, F. Roemer. Lethsea Geognostica, 1 Theil, p. 304. 



Not Tetragonis, Eichwald, 1842. Urwelt Russlands, Heft 2, p. 81. 

 1883. Dietyophyton, Barrois. Sur les Dictyospongidse des Psammites du 



Condroz, p. 85. 

 1890. Dictyophyton, Hall. Ninth Ann. Kept. N. Y. State Geol., p. 56. 



Very gradually expanding, smooth, obconical or subcylindrical sponges 

 with the outer surface devoid of nodes, tufts, ridges, annulations or other orna- 

 mentation; prism-faces sometimes very obscurely developed toward the 

 summit ; base furnished with a tuft of long, straight anchoring spicules. 



Type, Dictyophyton sceptrum, Hall. 



The fossil described by McCoy, (op. ait.) as Tetragonis Danhyi,* from the 

 upper Ludlow rocks of Westmoreland, appears, from the description and figure 

 given by the author and subsequently by Dr. Hinde, to be a reticulate sponge of 

 this genus. In regard to the nature of the oi'iginal species of Eichwald's genus 

 Tetragonis (T. Murcliisoni, Eichwald), we may accept the opinion of Hinde, 

 who says : " From an examination of undoubted forms of Tetragonis from the 

 Silurian of Gotland, I believe that it is a sponge, and that it is very closely 

 allied to Ischadites, Murch." 



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* Diciyospougia Danhyi^ see page 63 of this volume. 



