PLATE VI. 



Pigs. 1, lfl — 1 1, 2, 2 a — 2 k. — Hyalostelia Smithii, Young and Young, sp. 



Kg. 1. — A fragment of the dermal layer of the Sponge, showing the larger spicules in their 

 natural position with respect to each other. Enlarged ten diameters. Lower Carboniferous, upper 

 part of the Lower Limestone series at Cunningham Baidland, Dairy, Ayrshire. The original specimen 

 in the collection of Mr. John Smith, Kilwinning. 



Figs. 1 a — 1 Z. — Detached spicules of the skeleton and of the dermal layer. All enlarged to the 

 same scale of ten diameters. 1 a represents a spicule of the dermal layer in which the sixth or distal 

 ray is reduced to a small knob. In figs. 1/, lg, five of the rays are similarly reduced. From the same 

 locality and horizon, and in the same collection as the preceding. 



Fig. 2. — A fragment of the anchoring-rope of the Sponge, composed of elongated spicular-rods. 

 Partially embedded in a slab of limestone. Natural size. From Carboniferous Limestone (Toredale 

 series), near Richmond, Yorkshire. The original specimen in the British Museum (Natural History). 



Fig. 2 a. — A transverse section of a portion of the same specimen, showing the spicular-rods in 

 section. The clear circular spaces in the centre of each indicate the axial canals. Enlarged ten 

 diameters. 



Fig. 2 b. — A portion of a longitudinal section of the same specimen, showing three of the spicular- 

 rods with the axial canal in the centre of each. The intervening dark bands consist of the calcareous 

 matrix. Enlarged ten diameters. 



Fig. 2 c. — A fragment of a detached spicular-rod, showing the central axial canal and parallel 

 lines of growth. Enlarged ten diameters. From Law Quarry, Dairy. The original specimen in the 

 collection of Mr. John Smith. 



Figs. 2 d — 2 k. — Detached fragments of the anchoring spicular-rods showing the four recurved rays 

 at their distal extremities. All enlarged ten diameters. Lower Carboniferous at Low Baidland and 

 Cunningham Baidland, Dairy, Ayrshire. The original specimens in the collection of Mr. J. Smith. 



Figs. 3, 3 a — 3^. — Hyalostelia paballela, M'Coy, sp. 



Figs. 3, 3 a — 3 c. — Detached five-rayed spicules probably belonging to the dermal layer of the 

 Sponge. Enlarged twenty diameters. From Carboniferous Limestone at Ben Bulben, Sligo, Ireland. 

 The original specimens in tbe collection of Mr. J. "Wright. 



Fig. 3 d. — Fragmentary bundles of spicular-rods forming the anchoring-rope of the Sponge. 

 Exposed on the surface of a slab of dark limestone. Natural size. From Carboniferous Limestone, 

 Clogher, Tyrone, Ireland. Drawn from part of the type specimen of Serpula socialis, Portl., now in 

 the Museum of the Geological Survey, Jermyn Street. 



Fig. 3 e. — A transverse section of one of the anchoring-ropes, showing great variation in the 

 thickness of the component spicules. Enlarged ten diameters. From Carboniferous Limestone at 

 Clitheroe, Lancashire. The original specimen in the British Museum. 



Fig. 3/. — Transverse section of one of the spicular-rods in 3 e, showing tbe central axial canal 

 and concentric circles of growth. Magnified sixty diameters. 



Fig. Sg. — The distal extremity of one of the spicular-rods, showing the four recurved rays. 

 Magnified twenty diameters. From Ben Bulben, Sligo. The original specimen in the collection of 

 Mr. J. Wright, Belfast. 



