254 DR. HINDE AND MK. HOLMES ON SPOjSTGE-EEMAINS 



deposit is the retnarkable preponderance in the number o£ genera 

 and species of Monactinellid sponges over those of other groups. 

 In the cases of sponge-beds in Cretaceous and Jurassic strata 

 which have been hitherto investigated, the proportions have been 

 reversed, and it might be said that Tetractinellid, Lithistid, 

 and Hexactinellid spicules prevail almost exclusively, whilst 

 those of Monactinellid sponges appear to be absent. This 

 difference in the relative proportions of these groups is probably 

 due to the fact that in the Oamaru deposit the minute and 

 delicate spicules of Monactinellid sponges have been preserved 

 equally as well as the larger and more resistant spicules of the 

 other sponge-groups. Under similar conditions of preservation to 

 those of the sponge-beds of the Cretaceous and older rocks, nearly 

 all the Monactinellid spicules similar to those in the Oamaru 

 deposit would have been rendered unrecognizable ; and it is not 

 unreasonable therefore to suppose that the absence of these 

 sponge-spicules in the older rocks is rather due to their having 

 perished in the fossilization, than that they did not co-exist with 

 those other groups whose remains have been in part preserved. 



The neare.-t existing relatives of many of the sponges in this 

 New Zealand Tertiary deposit now^ inhabit the Indian and 

 Southern Ocean, some are cosmopolitan in distribution, whilst 

 others have as yet only been recognized in the North Atlantic 

 and the Oulf of Mexico. 



Another important fact is the association in this Oamaru de- 

 posit of sponge-reniains, which, judging by their nearest living 

 representatives, inhabit abyssal depths, with others, whose re- 

 lations now exist in comparatively shallow water. Thus, for 

 example, the deposit contaijis numerous spicules of the genus 

 Hi/ alonem a, recent i'oTvas of which, according to the ' Challenger ' 

 Eeport, usually occur in depths below 1000 fathoms, and range 

 down to 3000 fathoms. There are also spicules belonging to 

 such deep-sea Monactinellid genera as Cladorhiza, Chondrocladia, 

 and Ssperiopsis, species of vvhich were met with by the ' Chal- 

 lenger ' at depths from 1600 to 8000 fathoms. On the other 

 hand there are, in the Oamaru deposit, spicules of such genera 

 as Myxilla, which in recent seas are found in water not more 

 than 10 fathoms deep, though some species occur at 600 fathoms, 

 and of other genera both of Monactinellid and Tetractinellid 

 sponges, which now inhabit depths from 10 to 200 fathoms. 

 This association in the same deposit of the remains of what 



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