240 . DE. HINDE AlsD ME. HOLMES OK SPONGE-EEMAIKS 



III. LITHISTID^. 

 Body-Spicules of LitMstid Sponges. 

 Lyidium (a). — PI. XIII. figs. 25, 26, 27. Spicules of various 

 forms, witt an elongate, subcylindrical main axis, usually curved, 

 winch bifurcates or gives off lateral branches, terminating either 

 with transverse convex expansions or obtusely. Surface smooth. 

 Without axial canals. Length of spicules from '42 mm. to 

 '81 mm., thickness of axis "08 mm. to "122 mm. These spicules 

 are of the usual types present in Megamorine sponges, such as, 

 for example, Doi'yderma, Zitt., and other allied fossil genera. 

 They are smaller than the spicules of the recent genus Lyidium, 

 0?c. Sch. These forms are not very abundant in the Oamaru 

 material. Fossil spicules of the same character are present from 

 the Carboniferous upwards, and they are very common in the 

 Lower and Upper Grreensand and the Upper Chalk of the South 

 of England. They appear to be scarce in recent seas. 



Body-Spicules of Vetulina, Osc. Schmidt. 



Vetulina Oamarnensis, n. sp. — PI. XIII. figs. 31, 32, 33. Spi- 

 cules with definite centres, either rounded or irregular in form, 

 from which a variable number, generally from five to seven, short, 

 thick, straight or curved rays or branches are given off in dif- 

 ferent directions. The rays are usually simple, but occasionally, 

 as in fig. 33, they are bifurcate, and they terminate in lobed and 

 saddle-shaped expansions. In some spicules the centres have 

 stout conical spines as well as rays, and the rays themselves are 

 sometimes armed with spines. No canals can be distinguished. 

 The spicules range from "14 to '2 mm. in diameter, the centres 

 are about "05 mm. in thickness, the rays are from '051 mm. to 

 •075 mm. iu length. 



These spicules are of the Anomocladina type ; they correspond 

 with those of the fossil genus Mastosia, Zitt., and the recent 

 Vetulina, Osc. Sch., but they indicate a distinct species, which 

 may be termed Vetulina Oamaruensis. Sponges with this type 

 of spicule are not uncommon in the Jurassic strata of Germany, 

 they are rare in the Cretaceous rocks, and only one existing 

 species, V. stalactites, Osc. Sch. (Mexican Spong. p. 19, pi. i. 

 fig. 1, pi. ii. fig. 9), from off Barbados at 100 fathoms, is as yet 

 known. 



