IN" THE LOWER TERTIARY STRATA OF NEW ZEALAND. 241 



Sodif-Spicules of Tetracladine Lithistid Sponges. 



PL XIII. figs. 28, 29, 30. Spicules with four rays, usually 

 unequal in length, which, occasionally subdivide and terminate 

 obtusely. The rays are throughout studded with prominent 

 tubercles. The spicules are from -22 to "48 mm. in length, aud 

 the principal rays about '066 mm. in thickness. These spicules 

 are of the same character as those of the Cretaceous genus Flin- 

 tliosella, Zittel, and of the recent Discodermia, Bocage. 



Dermal Spicules of LitMstid Sponges. 



Corallistes (a). — PI. XIV. figs. 1, 7. Spicules with short coni- 

 cal shaft and horizontally extended head, consisting of six simple, 

 narroM^, obtusely pointed rays, resulting from the bifurcation of 

 the normal three rays. Axial canals extend throughout the rays 

 and open at their ends. Width across head of spicule from 

 •15 mm. to "SG mm. Spicules of similar character form the 

 dermal layer in Heterostinia, Zitt., and other genera of fossil 

 Cretaceous sponges, and in the recent Corallistes, Osc. Sch. 

 (Atlant. Spong. p. 22, pi. iii. fig. 3). 



Corallistes (b). — PI. XIV. fig. 6. Spicule with rudimentary 

 shaft and horizontal head of six flattened rays. Diameter of 

 head "5 mm., length of secondary rays '22 mm., width "07 mm. 

 This form is very abundant. Similar spicules occur in Thamno- 

 spongia and other Cretaceous genera, and in the recent genus 

 Corallistes. 



Theonella (a). — PI. XIV. fig. 4. Spicule with short shaft and 

 three flattened, horizontally extended head-rays, one simple and 

 rounded at the end, the others slightly furcate. Diameter of 

 spicule "8 mm., width of rays •125 mm. No canals are visible in 

 this form. Somewhat similar spicules are present in the recent 

 genus Theonella, Gray. 



Discodermia (a). — PI. XIV. figs. 2, 3, 5. Spicules with reduced 

 shafts and widely expanded head, in which the normal rays are 

 much subdivided. The rays are smooth, compressed, and end 

 obtusely. An axial canal is present in the shaft, but the canals 

 of the head-rays are quite rudimentary. Diameter of spicules 

 •9 mm., thickness of primary rays ^075 mm. Spicules of this 

 character are very abundant in the Lower and Upper Grreensand 

 and in the Upper Chalk of the South of England, but, as in this 

 Oamaru deposit, they are detached irom the sponges to which 



LINN. JOUKN. — ZOOLOGY, VOL. XXIV. 17 



