IN THE LOWEH TERTIARY STRATA OP NEW ZEALAND. 237 



radiate from a common centre. In most forms there is one canal 

 in the form of a loop or curve. Not infrequently the canals are 

 so fine as to be only |)artially visible. 



This form of spicule was first described by Mr. Carter from 

 the Upper Greensand of Devonshire, and similar spicules have 

 subsequently been described from the U|>per Chalk of AVest- 

 phalia and Norfolk. They have been figured by Dr. Eiist from 

 the radiolarian Jurassic marls of Ilsede, Hanover (' Palseonto- 

 grapliioa,' Bd. xxxi. pi. xx. fig, 42) ; and they also occur in the 

 Tertiary radiolarian earth of Barbados (Bury, ' Polycystines in the 

 Barbados Chalk Deposit,' 1862, pi. vii. figs. 1,2) ; and Ehrenberg 

 has figured an imperfect specimen said to have been dredged up 

 from a depth of l;3,200 feet in the Indian Ocean between Zanzibar 

 and the Seychelles (Microgeol. Studien, 1873, p. 147, pi. 36. 

 fig. 9), to which he gave the name of Placolithis lacunosa. A 

 detached spicule also occurs in the ' Egeria ' dredgiugs off the 

 S.W. coast of Australia at a depth of 3000 fathoms. Hitherto 

 no recent sponge has been discovered with similar spicules. It 

 seems probable that they may be dermal spicules, but they are of 

 quite a difterent character from the globates of Geodia or the 

 discoidal spicules of I]ryJus. The Oamaru forms are smaller, and 

 show a greater variation in outline than those from the Upper 

 Chalk. 



Gldbostellnte Spicules loitJi truncate and lohed rays. 



Stelletta (b).— PI. XIV. figs. 28, 29. Spicules subspherical in 

 outline, consisting of a solid centre or nucleus from which 

 numerous short rays or arms project in difi'erent directions. The 

 rays are stout, subcylindrical, with truncate and expanded 

 summits, usually divided into lobes. In each ray there is an 

 axial canal. The spicules appear to have been interlocked to- 

 gether by means of the lubate ends of the rays. Total thickness 

 of spicule "1 mm. ; length of rays '025 mm., thickness '018 mm. ; 

 width of their summits from "02 to '026 mm. These spicules 

 resemble in character the globostellates of Stelletta intermedia, 

 Osc. Sch. (Algier. Spong. 3rd Supp. p. 21, pi. iv. fig. 6), but the 

 arms are shorter and their summits more expanded. According 

 to Schmidt, the rays of these recent spicules intergrow together. 

 Somewiiat similar, but much smaller, spicules are also pre.-^ent 

 \v\. Stelletta reticulata. Carter (^Ann. &Mag. Nat. Hist. s. 5, vol. xi. 

 1883, p. 352, pi. xiv. fig. 4 e), from off the S. coast of Australia. 



