246 BRITISH JURASSIC SPONGES. 
alate, or irregular in form, sessile or with a short pedicle, the base flattened or 
concave, and with a dermal layer, which in some cases extends over the lower 
part of the sponge. The upper portion of the sponge is seamed by a series of 
deeply impressed furrows, which radiate from the summit, and between them are 
ridges, lobes, or wing-like flanges, which are occasionally laterally corrugated. 
The sponge is built up of reticulate fibres, which are very thick in the central 
portions, but slender and open near the exterior. The fibres consist of medium- 
sized three-rayed spicules, sometimes in a single series or but slightly over- 
lapping each other, but more closely grouped together in the central portion of the 
flanges or ridges. There is no cloacal tube nor definite canals. 
The peculiar form and the absence of a cloacal tube and special canal system 
readily distinguish this genus. The type-species, Blastinia (Achilleum) costata, 
Goldfuss, sp., is from the Middle Jura of Streitberg, Wiirtemberg (‘ Petref. Germ..,’ 
vol. 1, p. 94, pl. xxxiv, fig. 7). 
54. Buasrinta costata, Goldfuss, sp. Plate XIX, figs. 5—5 ce. 
1826—33. ACHILLEUM cosTaTUM, Goldfuss. Petref. Germ., vol. i, p. 94, pl. xxxiv, 
fig. 7. 
1878. Buastrnia costata, Zittel. Studien, Abth. 3, p. 182. 
1884. _ cristata, Hinde. Quart. Journ. Geol. Soc., vol. xl, p. 781, 
pl. xxxv, figs. 83—3 b. 
Sponges small, simple, hemispherical, depressed-conical or oval in outline, 
base flattened, or concave when growing on a convex object, with a rugose 
dermal layer, which in some instances covers the lower portion of the sponge. 
From the summit a variable number, generally from five to nine, deep depressions 
extend to near the base, and between these is a corresponding number of rounded 
ridges. The surface of the ridges merely shows small irregular apertures 
between the fibres. As seen in a transverse section of the sponge the fibres 
follow a linear arrangement, radiating from the central area. They are, as a rule, 
delicate, about ‘03 mm. in thickness, but near the ridged portions they become 
very considerably thickened, and reach -32 mm. in width. They consist of 
apparently subequal three-rayed spicules, the rays of which are from ‘12 mm. to 
‘17 mm. in length, and about ‘05 mm. in thickness. 
The examples of this species are all of small dimensions, ranging from 3 mm. to 
7°5 mm. in height, and from 3 to 8 mm. in diameter, and thus they are somewhat 
smaller than Goldfuss’s figured type, which is 10 mm. in height. In the character 
and number of the ridges our specimens correspond with the type-species, and I do 
not now see sufficient grounds to regard them as distinct, though from a misunder- 
