IN THE LOWER TEETIAET STRATA OF IfEW ZEALAND. 253 



PI. XIV. fig. 38. Spicule having the form of a delicate thin 

 plate, elliptical in outliue, with smooth margins, within this is 

 a narrow band inclosing an ellipse with a slight central con- 

 striction ; nearly in the longer axis of this figure is a short 

 straight axial canal with a slight bead-like inflation near one end, 

 and on either side of this a simple canal shorter than the central 

 one. The inner band has a finely crimped exterior margin. 

 Length of spicule '105 mm., width -06 mm. This is a rare form 

 and its aflfinilies are very doubtful. 



General Summary. 



As the result of our investigation of the material from Oamaru, 

 we find that the probable number of genera and species of the 

 different divisions of siliceous sponges, as represented by their 

 detached spicules, is as follows : — 



Monactinellid, 70 species and 24 genera. 

 Tetractiuelhd, 22 „ „ 9 „ 

 Lithistid . . 7 „ „ 5 „ 

 Hexactinellid, 11 „ „ 5 „ 

 thus giving a total of 110 species and 43 genera which can be 

 definitely recognized. These numbers in all probability fall far 

 short of the real number present in these beds of siliceous rock, 

 for account must be taken of the fact that only a mere handful 

 of material has been so far examined, and this has been taken at 

 random from the deposit, which, as already stated, is in one 

 place from 40 to (JO feet in thickness. The number of species 

 also would have been increased if an estimate could have been 

 made of those whose skeletons only consist of the common types 

 of larger spicules without distinctive flesh-spicules. These 

 simple types of skeletal spicules, more particularly of Monac- 

 tinellid sponges, are very abundant in the deposit, but they aff'ord 

 no data of the species or particular genus which they represent, 

 and do not therefore appear in the summary. Nearly every 

 hitherto known form of spicule of siliceous marine sponges, both 

 skeletal and fl.esh-spicules, is represented in the Oamaru de- 

 posit, if we except some of those from Palaeozoic strata and a few 

 of recent sponges. Whilst the detached spicules ap{)ear for the 

 most part to belong to still existent genera, the species, so far 

 as can be determined from the flesh-spicules, are probably, with 

 a few exceptions, distinct from recent forms. 



A particular feature in the sponge-fauna of this Oamaru 



