IN THE LOWEll TKETIART STRATA OV NEW ZEALAND. 183 



spicules tinder the groups of the Mouactinellidse, Zittel (or 

 Monaxonida, Eidle}'^ & Dendy), Tetractinellidao, Marshall, Lithis- 

 tidse, Osc. Schmidt, and Hexactinellidse, Osc. Schmidt. 



I. MONACTINELLID^, Zittel 

 (=Monaxonida, Ridley Sf Dendy). 



In this division, which appears to have been more numerously 

 represented than any other, the characteristic acerate, cylindrical, 

 acuate, and pin-shaped skeletal spicules are very abundant and 

 exhibit numerous gradations of size, and there is a considerable 

 variety of the anchorate, hook-shaped, and sceptre-like flesh- 

 spicules. The skeletal spicules of this group are as a rule such 

 bimple forms and common to so many genera as to be of little 

 service in classification, but the minuter flesh-spicules, many of 

 which are so small as to require to be figured on the scale of 600 

 diameters, alfordgood generic and specific indications. Hitherto 

 so little has been known of fossil sponges of this group, that it 

 has been supposed that they did not exist in any numbers in 

 earlier epochs ; but the evidence from this deposit shows that in 

 the New Zealand region they abundantly flourished during the 

 Early Tertiary period, and that they were proportionately as 

 numerous and as varied as at the present day. 



SJceletal Spicules o/'Eeniera, Chalina, and allied Genera. 



PI. VII. figs. 1, 2. Smooth acerates, slightly curved, slender, 

 ranging from '106 to "15 mm. in length by "005 to "009 mm. in 

 thickness. 



PI. VII. figs. 3-8. Smooth acerates, curved, fusiform, stouter 

 than the preceding, varying between "MS and "37 mm. in length 

 by •013-'03 mm. in maximum thickness. Spicules of similar 

 forms and proportions to these are very generally present in 

 existing species of Seniera and Ohalina. 



PI. VII. figs. 9, 10. Smooth, slender acerates, fusiform, very 

 elongate, straight or sinuous, one end sometimes tapering more 

 rapidly than the other. Length •9-l"14 mm. by •015-*02 mm. 

 in thickness. Similar spicules are figured by Eidley and Dendy 

 in Halichondria latrunculioides (Chall. Rep. vol, xx. p. 6, pi. ii. 

 fig. 1), from off" the Eio de la Plata at a depth of 600 fathoms. 



PL VII. figs. 11-13. Acerate spicules with nearly straight, 

 smooth, cylindrical shafts and abruptly-pointed extremities. 



