LYMNORELLA INCLUSA. 237 
Base flattened, concave, or with a short stem, and enclosed by a rugose dermal 
layer, which sometimes also wraps round the sides as well. The upper surface 
exhibits minute apertures between the fibres, and occasionally small shallow 
depressions with one or more circular or elongate apertures connected with 
shallow canals, which appear to represent the oscules; but in some specimens all 
traces of oscules and distinctive canals have disappeared, and the circulation 
must have been carried on in the interspaces of the mesh. Vertical sections 
show concentric zones of growth, which are also marked by bordering bands of 
the dermal layer on the outside of the sponge. 
The skeleton fibres are of a somewhat coarse character; in some portions they 
are materially thickened: they range from ‘12 to ‘24 mm. in thickness. The 
fibres are in the same crystalline condition as in the previous species; in the 
thickened portions the axial spicules are more numerous and more closely arranged 
(Pl. XVIII, fig. 3c): the spicular rays range up to ‘3 mm. in length by :036 mm. 
in thickness. Slender tuning-fork spicules are likewise present in the fibres; a 
perfect specimen is *2 mm. in length (Pl. XVIII, fig. 3d). Very minute three- 
rayed spicules can also be seen in the dermal layer. 
There is great difference in the forms of this species. Some examples are 
nearly round, others top-shaped, whilst others grow in flattened or irregular 
nodose masses, consisting of successive layers, overlapping each other either 
partially or entirely. These range from 20 mm. to 80 mm. in thickness. In many 
no special canals or oscules can be seen, and the genus Inobolia was proposed to 
include these ; but there are specimens in which here and there oscular apertures, 
connected with short open furrows or canals, are developed, thus showing inter- 
mediate stages in the canal system, so that no generic distinction can be made on 
this ground. The distinction between this species and L. mamillosa rests on the 
absence of ostia, the absence or slight development of the canals, and the coarser 
fibres. It is probably allied to L. gigantea, Michelin (‘Icon. Zoophy.,’ p. 247, 
pl. lviii, fig. 7), but the description given of this form is insufficient to allow of a 
definite comparison. 
Distribution.—Inferior Oolite. Pea-grit series, Crickley Hill and Cleve Hill, 
near Cheltenham. ‘Trigonia-grit, Leckhampton (Mr. R. F. Tomes). The type- 
specimen is in the British Natural History Museum, South Kensington, and there 
are also specimens in the museums at Jermyn Street and at York. 
