122 BRITISH PALAMOZOIC SPONGES. 
marked out by delicate curved ridges, which cross each other with great regularity, 
and thus form rhomboidal, slightly depressed areas, which represent the spaces 
occupied by the summit-plates of the spicules. Within each of these areas the 
cross formed by the four transverse rays can be distinguished (PI. II, fig. 1 6), and 
occasionally at the centre of this a small circular aperture indicates the entering 
ray of the spicules. In other conditions of preservation the rhomboidal areas are 
not shown, and the surface of the specimen exhibits only the vertical and concen- 
tric lines formed by the transverse spicular rays (PI. II, fig. 1 a). 
Mr. Salter’ has figured this species with a short stem and diverging rootlets, 
and he has stated that specimens possessing these appendages occur at Llangollen. 
I have not met with any example in the museums at Cambridge or at Jermyn 
Street showing the least indications of these structures, and it is evident from 
their absence in the remarkable perfect specimens from the Isle of Gothland, which 
were kindly lent to me by Prof. G. Lindstrém, of Stockholm, that Mr. Salter’s 
figures are purely diagrammatic. 
The type of this species, and of the genus as well, is preserved in the museum 
of the Geological Society, Burlington House. It shows the casts of several 
individuals on a slab of hard, biuish, caleareous shale. In common with other 
members of this family, considerable numbers of these Sponges appear to have 
generally lived in close association with each other. The types of Ischadites 
antiquus, Salter, and I. tessellatus, Salter, both in the Museum of the Geological 
Survey, Jermyn Street, do not appear to me to be separable from I. Kanigit. 
Distribution.—Ordovician : Lower Llandeilo; Garn, Arenig Mountain, Wales. 
Caradoc; also in Galena Beds; at Seale’s Mound, Illinois, andin Iowa. Orthoceras 
Limestone; Reval, Esthonia. Silurian: Woolhope Beds; Malvern; near Build- 
was, Shropshire. Wenlock shales and limestones; Dudley, Usk, Malvern, 
Walsall, Balcletchie, Penkill, Ayrshire. Lower and Upper Ludlow; Ledbury, and 
near Ludlow; Pentland Hills, Scotland; Visby, Westergarn, near Klintehamn, 
Djupvik, Isle of Gothland; Niagara Group; Waldron, Indiana; Yellow Springs, 
Ohio; Lower Helderberg Group; Gaspé, Province Quebec. 
' «Cat. Cambrian and Silur. Foss. Cambridge,’ p. 100. 
