134 MR. 0. W. A.WDBEWS VXD OTHEES OH THE [Feb. 20, 



only the inner third, where they are divided into two zones by a 

 shallow space. 



/Spicules. Megascleres — strongyloxea, 1330x35ju. 



Microscleres — spherasters, 60 p. Somal chiaster3, 15-18^. 

 Dermal chiasters, 12 /i. 



The unique specimen measures 2*5 X 2 c.c. in horizontal and 2*5 c.c. 

 in vertical plane. The rough convex under surface appears to have 

 been torn off from a rock. 



The name given to the species denotes its close affinity to 

 T.japonica Sollas ; it differs from the latter (1) in its mode of 

 growth, T. japonica being spherical and free, (2) in having the 

 membranous oscular cones, and (3) in the slight difference in size 

 between the dermal and soraal chiasters. 



Spirastrella carnosa Topsent. 



1897. Spirastrella carnosa Topsent (18. p. 441). 



The specimen is cauliflower-shaped, expanding upwards from a 

 narrow base to a height of 2 c.c, the area of the upper surface 

 being 2-5 x 1*5 c.c. The upper surface is covered with low 

 rounded papillae. 



The tylostyles, 525x18 /j, usually have a trilobate head. The 

 spirasters are extremely rare and very fine, being 18 X 1 p, with 

 minute spines, and usually with four curves. 



The specimen differs from the type from Amboina in having 

 larger megascleres, these being only 330 x 6 to 8 ^ in the latter. 



In Topsent's specimens, too, the surface is ridged (" fronce "). 



Distribution. Amboina ; Christmas Island. 



Spirastrella decoibens Ridley, var. robusta, var. nov. 



1887. Spirastrella decumbens var., Ridley and Dendy (13. 

 p. 229, pi. xlv. fig. 12). 



1898. Spirastrella semilunaris Lindgren (10. p. 323, pi. xix. 

 fig. 23). 



There are two specimens of this variety — one (1) forming a thin 

 yellow crust on a shell, the other (2) in the form of small fleshy 

 lobes growing on Sidonops picteti. Specimen (1) has a shallow 

 patent oscule l'fi mm. in diameter; the surface shows a delicate 

 reticulate pattern formed by the pore-areas, the pores being 

 circular and 40 fi iu diameter ; sieve-like groups of 5 to 10 pores 

 lead into subdermal spaces. 



A cavernous cortex from - 5 to 1 mm. in thickness occurs in the 

 type specimens of the species from Torres Straits, described bv 

 Ridley (11. p. 470, pi. xliii. fig. c). The same structure is al>o 

 present in the specimens from Amboina and Christmas Island. 

 In all these specimens the minute semilunar spirasters (12 p in 

 length) form the outermost dermal layer. Hence I have no 

 doubt that Lindgren's species is a synonym : at the same time it 

 is right to add that that author is in no way to blame, owing 

 to the incomplete description of the type specimens, which are 

 badly preserved. 



