MYRMECIUM BIRETIFORME. 233 
others a low ridge crossing the grooves ; canals from the interior open into the 
grooves. ‘The surface of the sponge between the grooves has irregularly scattered 
oval or circular ostia from -25 mm. to “45 mm. in width, as well as pore-like inter- 
spaces between the fibres. The spicular structure is similar to that of H. bella. 
The examples of this species are all very small, varying from 4 mm. to 6 mm. 
in height and from 3°5 mm. to 7 mm. in thickness. The dermal layer is limited 
to the base of the sponge ; in one specimen it is seen to consist of slender three- 
rayed spicules : the rays are from ‘015 mm. to ‘03 mm. in length (Pl. XVII, fig. 7 d). 
The peculiar feature in this species is the manner in which the summit is deeply 
cleft, so as to give it roughly the appearance of a mitre. The ostia are only seen 
in the best preserved examples (Pl. XVII, figs. 7, 7 c.) 
Distribution —Inferior Oolite. Parkinsoni-zone at Shipton Gorge (Mr. E. 
A. Walford), and from the Marl-bed at Bradford Abbas, Dorset (Mr. R. F. Tomes). 
Genus.—Myruectum, Goldfuss. 
1826-88. Petrefacta Germaniz, vol. i, p. 18. 
Syn.—Cnemidium, Goldfuss (nm part) ; Spongites, (Juenstedt (in part) ; Epitheles, 
Fromentel (in part). 
Small simple sponges, spherical, hemispherical, or cylindrical, attached by a 
flattened base or small pedicle ; base, and sometimes the lateral surfaces as well, 
with a corrugated dermal layer. Summit rounded with a central oscule, from which 
radiating open furrows are given off. A tubular or funnel-shaped cloaca, into 
which the radial canals open. Outer surface with pore-like ostia. The skeletal 
fibres delicate. The type species is Myrmecium hemisphxricum, Goldfuss, from the 
Upper Jura of Thurnau (‘ Petref. Germ.,’ vol. i, p. 18, pl. vi, fig. 12). 
42. Myrmectum prretirormn, Sollas. Plate XVII, fig. 8. 
1883. Myrmuercrtum BiretirorMe, Sollas. Quart. Journ. Geol. Soc., vol. xxxix, 
p. 550. 
The type-specimen referred to this species by Prof. Sollas is small, nearly 
spherical, attached directly by the base; the summit is depressed with a central 
circular osculum, from which a few inconspicuous open furrows radiate for a short 
distance. The outer surface exhibits pore-like irregular apertures between the 
