PLATE I. 



Figs. 1, 1 a. — Pbotospongia fenestbata, Salter. 



Fig. 1. — A fragment of the spicular-mesh of the Sponge-wall, embedded in hard black slate. 

 Natural size. From Menevian strata, St. David's, South Wales. Drawn from the type example of 

 the species, now in the British Museum (Natural History). 



Fig. la. — A portion of the spicular-mesh of the same specimen, magnified five diameters. The 

 original regular arrangement has been partly broken up, and owing to the cleavage of the rock the 

 angles of the spicules are distorted. 



Figs. 2, 2 a. — Peotospongia Hicksi, Hinde, sp. nov. 



Fig. 2. — The compressed Sponge-wall, traces of which can be seen covering the surface of a slab 

 of dark shale. Natural size. From Menevian strata, Porth-y-Bhaw, St. David's, South Wales. 

 Drawn from the type specimen, in the Woodwardian Museum, Cambridge. 



Fig. 2 a. — Portion of the spicular-mesh of the same specimen in an imperfect condition. Magni- 

 fied five diameters. 



Figs. 3, 3 a, 3 b.— Htalostelia fasciculus, H'Coy, sp. 



Fig. 3. — Portion of the anchoring-rope of the Sponge, showing the parallel disposition of the 

 component spicules. Natural size. Probably from Llandeilo Bocks. Original in British Museum 

 (Natural History). 



Fig. 3 a. — Transverse section of the same specimen, enlarged ten diameters. 



Fig. 3 b. — Portion of the rope, enlarged ten diameters, showing the annular or spiral frills on the 

 spicules. 



Figs. 4, 4 a. — Htalostelia Smithii, Young and Young, sp. 



Fig. 4. — Portion of the rock, showing the size and the distribution of the anchoring-spicules 

 in transverse section. Magnified five diameters. From Ordovician shale at Knockgeiran, near 

 Grirvan, Ayrshire. The original specimen in the collection of the author. 



Fig. 4 a. — A longitudinal section of the rock, showing the spicules, which have been cut through 

 obliquely. The transverse bands in them arise from the replacement of the silica by a mineral of a 

 different aspect. Magnified five diameters. 



Figs. 5, 5 a — 5/. — Htalostelia gbacilis, Hinde, sp. nov. 



Figs. 5, 5 a— c. — Hexactinellid spicules, with the normal number of rays, though mostly imperfect. 



Figs. 5 d, e. — Cruciform spicules, rays all unequal. In 5 e they are spinous. 



Fig. 5f. — Microspined cylindrical rods, probably belonging to the anchoring spicules of the Sponge. 

 All magnified forty diameters. From decayed Wenlock limestones, Craven Arms, Shropshire. The 

 original specimens in the collection of John Smith, Esq., Kilwinning, Ayrshire. 



Figs. 6, 6 a — 6 d. — Ateactosella silubiensis, Hinde, sp. nov. 



Detached fusiform spicules, referred to this species. The specimens are siliceous; Ga, b, are 

 partially encrusted with matrix. Magnified forty diameters. From Wenlock limestones, Craven 

 Arms, Shropshire. The original specimens in the collection of John Smith, Esq., Kilwinning. 



Figs. 7, la — 7 d. — Astejeospongia patina, F. Soenier. 



Detached spicules of this species, the rays in all cases imperfect. In Figs. 7 a, b, c, only the six 

 horizontal rays are present, in Fig. 7 one ray of the vertical axis is developed, whilst 7 d represents an 

 abnormal form in which only half the number of the horizontal rays is developed. Magnified forty 

 diameters. From Wenlock shales at Wren's Nest, Dudley, and at Benthall Edge, Shropshire. The 

 original specimens in the collection of John Smith, Esq., Kilwinning. 



