122 BRITISH PALEOZOIC 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 (PL II, fig. 1 b), 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 1 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. Lindstrom, 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, bluish, calcareous 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. Koenigii. 



Distribution. — Ordovician : Lower Llandeilo ; Garn, Arenig Mountain, Wales. 

 Caradoc; also in Galena Beds ; at Seale's Mound, Illinois, and in 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 ; Yisby, Westergarn, near Klintehamn, 

 Djupvik, Isle of Gothland ; Niagara Group ; Waldron, Indiana ; Yellow Springs, 

 Ohio ; Lower Helderberg Group ; Gaspe, Province Quebec. 



1 ' Cat. Cambrian and Silur. Fobs. Cambridge,' p. 100. 



