244 DE. HINDE AND ME. HOLMES ON SPOMGE-EEMAINS 



exceed those of other kinds and constitute the large majority of 

 spicules present. Most of the Tetractiuellidse belong to genera 

 well represented in the Cretaceous and even older rocks, as well 

 as existing at the present day ; other genera, such as Gorticium 

 and PlaJcina, are rare at present and restricted in their distri- 

 bution. Lithistid sponges are but sparsely represented ; two of 

 the three genera recognized, Lyidium and Vetulina, are rare in 

 the present day, but they belong to families which date back 

 from the Carboniferous epoch. In comparison with the number 

 of species in the Oamaru deposit, it may be mentioned that the 

 ' Challenger ' Expedition only obtained 25 species of Tetracti- 

 nellids from the entire South-Australian Eegion, in which New 

 Zealand is situate, and but a single species of Lithistid from the 

 same region (Chall. Eep. vol. xxv. p. 387). 



IV. HEXACTINELLID^, Osc. Schmidt. 



Acerate Spicule of Hexactinellid Sponge. 

 PL XY. fig. 1. Spicule straight, fusiform, with a slight sub- 

 central inflation, gradually tapering to either end ; surface with 

 minute spines, more numerous near the ends and sparse in the 

 central portion, they project at right angles to the surface. 

 An axial canal traverses the spicule and opens at either end ; in 

 the centre there is a distinct nodal swelling. Length of spicule 

 •48 mm., greatest thickness "015 mm. The central inflation of 

 the axial canal indicates that this form belongs to some hexacti- 

 nellid sponge. Acerate spicules, smaller than this fossil and 

 without spines, are present in the recent Euplectella nodosa, 

 Schulze (Chall. Eep. vol. xxi. p. 82, pi. xiv. figs. 3, 4), from near 

 the Bermudas. 



Pinule Spicules with Six JRays. 

 PL XV. fig. 2. Transverse and proximal rays of the spicule 

 subequal, straight or slightly curved, and minutely spined near 

 the ends ; the spines on the distal ray thickly set, projecting 

 upwards, the end of the ray extends beyond the spines. Length 

 of the distal ray '137 mm., width (including spines) '029 mm., 

 length of the other rays '069 mm., thickness '01 mm. Pinules 

 of similar form, but larger, are figured by Schulze in Aulascus 

 JoJinstoni (Chall. Rep. vol. xxi. p. 118, pi. xxii. fig. 3), from the 

 Indian Ocean at a depth of 310 fathoms. 



