Description of new Lower Silurian Sponges. — Ulrich. 235 
peculiarly modified hexacts, as shown in figures 2 and 4 of the 
accompanying cut. In figure 2 we have an arrangement some- 
what like that usual among the Dictyospongidce, and it is as 
an abnormal type of that hexactinellid family that I regard 
Rauf fella. I am not certain that R. palmipes ought to be 
considered as congeneric with R. Mosa, iheform of the sponge 
being very different in the two species . That they belong to 
the same family is scarcely to be questioned. 
The position of Leptopoterion, in the absence of a definite 
knowledge of the spicular structure, is somewhat doubtful. 
The general aspect, however, is suggestive of the Hexactinel- 
lidce, and indicates a relationship to the Dictyospongidw on 
the one hand and, perhaps less strongly, the ReceptaculitidcB 
on the other. The peculiar bodies which in one of my earlier 
papers were named Lepidolites and are now classed provis- 
ionally in the latter family, may be more closely related than 
would at first appear. 
Ueterospongia and Saccospongia.^ together with Dystacto- 
spongia S. A. Miller, and Strotospongia, a new genus described 
in my report on fossil sponges for vol. viii 111. Geol. Survey 
reports, (now in press) constitute a natural group of sponges, 
having, I believe, rather close relations to Calcisp)ongim of the 
type of Corynella Zittel. Sir epto spongia and Cylindroccelia 
are difficult to place. If I should hazard an opinion it would 
be that both belong to the Calcispongios^ the former near 
Dystactospongiaj the latter, perhaps, near Myrmecium 
Goldf. (Zittel). 
RAUFFEIiliA n. gen. 
Sponges free (?), forming hollow cylindrical stems, or ra- 
dially arranged leaves. Wall exceedingly thin, composed of two 
distinct layers of spicule-tissue. Inner layer minutely por- 
ous, the pores irregularly distributed, of unequal size, the 
larger ones rounded, the smaller ones much more numerous 
and mostly of irregularly angular outline ; spicular tissue sep- 
arating pores thin, the nature of its elements undetermined. 
Outer layer consisting of a network of large spicules, appar- 
ently of a curiously modified hexactinellid type. Usually 
they appear as irregularly coalescing thread-like stria? lining 
the surface in a longitudinal direction, with more slender con- 
necting filaments traversing the narrow intervening spaces at 
more or less acute angles leaving acutely elliptical depressed 
