IN THE LOWER TERTIARY STRATA OF NEW ZEALAND. 231 



•033 mm., of the shaft '025 mm.; length of summit-rays "OOSS 

 mm. lu the number of the summit-rays this form corresponds 

 with the spicules of Plakina trilopha, Schulze (Zeitsch. f. wiss. 

 Zool, Bd. xxxiv. (18S0) p. 407, pi. xxi. figs. 12 a, /3, ??), but the 

 rays in these latter are simply pointed. 



Pi. XII. fig. 21. Spicule with a singie, straight, tapering 

 shaft which bifurcates at the summit and gives off on either side 

 three pairs of short curved rays, with bifid ends. Length of 

 spicule "05 mm., of shaft -033 mm., thickness of shaft '003 ram. ; 

 length of summit-rays '01 mm. This and the preceding form 

 (fig. 20) probably belong to the same species, which may be 

 termed PlaTcina cmstralis. Spicules of this genus have not been 

 previously met with as fossil ; the existing forms are only known 

 from the Mediterranean. 



CaltJirops, or four-rayed Spicules o/Tachastrella, Osc. Schmidt. 



PI. XIII. fig. 35. Calthrops with three subequal rays and one 

 ray shorter than the others. Two of the rays are slightly fur- 

 cate, and two simple and pointed ; axial canals are present in 

 all. Longest ray '17 mm. by '023 mm. 



PI. XIII. figs. 36, 37, 38, 40. Calthrops spicules of difi'erent 

 sizes, with smooth simple rays, which vary in length from '023 

 to '23 mm., and in thickness from '0066 mm. to '075 mm. In 

 another specimen the rays are '8 mm. in length. 



Pi. XIII. fig. 39. Calthrops with rays unequal in length ; 

 th.ree are smooth, whilst the other is thickly set with small 

 conical spines, and in this ray alone is an axial canal visible. The 

 longest ray is '085 mm. by '001 mm. in thickness. 



As a rule the calthrops spicules in the Oamaru material are 

 much smaller than those which are present in the Cretaceous and 

 older rocks. They are fairly abundant in the coarser portions of 

 the deposit associated with the large trifid spicules of Geodites, 

 &c. 



Spined Calthrops Spicule of unknoion Sponge. 



PI. XII. fig. 37. Small calthrops spicule with short, conical, 

 obtuse rays, armed with strong projecting spines. Length of 

 rays "021 mm., thickness '005 mm. Detached spicules of a 

 similar character, but larger than these fossils, are figured by 

 Bowerbank in a recent undescribed sponge from Freemantle, 



