SPONGES. 217 



The Trenton period, including the rocks between the top of 

 the Calciferous and the base of the Silurian, introduces a largely 

 increased and much better preserved sponge fauna. The HEXACTI- 

 XELLIDA are represented here byCyathophycus,Rauffella,Brachio- 

 spongia, Hyalostelia, Calathium (pars), Leptopoterion, Recepta- 

 cuUtes. Lepidolites and isolated spicules of a genus probably iden- 

 tical with Astrseospongia; the LITHISTIDA by Hindia, Astylo- 

 spongia(?), Anthaspidella, Zittelella, Edriospongia, Streptosolen 

 and Aulocopium, the last by an undescribed species from the 

 upper beds of the Trenton limestone in central Kentucky; and 

 the CALCISPONGLE, probably, by Strotospongia, Saccospongia, 

 Dystactospongia, Cylindroccelia and Camarocladia in the Tren- 

 ton limestones of Illinois and Kentucky; and byDystactospongia, 

 Heterospongia . Strep tosp ongia and Cylin droccelia in the Cincinnati 

 rocks of Ohio and Kentucky. The systematic position of Pat- 

 tersonia S. A. Miller, which seems identical with the lately 

 proposed Strobilospongia of Beecher*; and of Eosp ongia, Bil- 

 lings, has not yet been determined. 



SILURIAN SYSTEM. Among Silurian deposits the Niagara group 

 offers a number of localities where fossil sponges abound. They 

 are most prolific in Western Tennessee, (Perry and Decatur 

 counties) where the surface of the ground is sometimes thickly 

 strewn with good specimens of Astylospongia, Palseomanon, 

 Astraeospongia, and Hindia, while the genera Aulocopium, 

 Climacospongia, and at least one other genus, occur more 

 rarely. None of the strata of this system below the Niagara 

 have, so far as I am aware, furnished remains of sponges. It 

 is. however, not at all unlikely that some at any rate of the 

 numerous "fucoids" of the Clinton will prove eventually to be 

 sponges and not plants. From above the Niagara, the Lower 

 Helderberg contains sponges at certain localities. Hindia 

 sphseroidalis Duncan (Astylospongia inornata Hall) is the 

 principal form. This species seems to be identical with the 

 common Niagara form of the genus. 



* Memoirs of the Peabody Museum of Yale University, vol. n, pt I, p. 14, 1889. In 

 this excellent contribution Mr' Beecher establishes the position of Brachiospongia. He 

 shows the genus to belong to the HexactineUidse and proposes a new family, Brachio- 

 spongidae, including, besides the type genus, also the new Strobilospongia^ 



27 



