70 BRITISH FOSSIL SPONGES. 
skeletal-spicules of Cnemidiastrum Hoheneggeri, Zitt. (Fig. 4, c), from Upper Jurassic 
strata at Cracow, and in species of Aulocopiwm, from Silurian strata in Gothland (Fig. 
4, d). This latter genus has indeed been placed by Zittel in the Tetracladina family, 
but in the character of its skeletal-spicules it appears to me more nearly to resemble 
Cnemidiastrum than any tetracladine genus. Rarely, also, in some of the Sponges 
of this family, spicules occur in which three subequal spinous rays radiate from a 
common centre, thus approximating in form to the tetracladine spicules. Zittel! 
has figured a spicule of this form from Hyalotragos patella, Goldf. sp. 
as a 
eas 
Fie, 4.—Various forms of fossil lithistid spicules belonging to the families of the Rhizomorina, 
Megamorina, and Anomocladina. (a) Branching, spinous, skeletal-spicule of rhizomorine lithistid, 
Seliscothon Mantelli, Goldf. sp. (4) Two skeletal-spicules of the same Sponge, showing their 
mode of union with each other. (¢) Skeletal-spicule of the rhizomorine Sponge, Cxemidiastrum 
Hoheneggeri, Zitt., from the Upper Jura of Cracow. (d) Skeletal-spicule of the rhizomorine 
Sponge Aulocopium, sp. from the Silurian of Gothland. (e) Skeletal-spicule of a megamorine 
Sponge, Doryderma, sp. from the Senonian strata of Coesfeld, Westphalia. (jf) Skeletal-spicules 
of Doryderma, showing their mode of union with each other. (g) Skeletal-spicule of the mega- 
morine Sponge, Carterella, sp. (hk) Portion of the skeletal mesh of the Anomocladina Sponge, 
Astylospongia, sp. from the Silurian of Gothland, showing the spicules and their mode of union 
with each other. 
(b) Megamorina—The skeletal-spicules of this family consist of a straight, or, 
more frequently, variously curved, elongated main axis, which may either be 
simple, or may give off irregular branches in different directions (Fig. 4, e, f, 9). 
The terminal ends of the main axis and of the branches either form tapering 
blunted processes, or more usually expand into flat or concave, spoon-shaped 
surfaces. Both the tapering extensions and the concave expansions may be 
1 «Studien ueber fossile Spongien,’ ii, Taf. 3, fig. 4. 
