REPORT ON THE TETRACTINELLIDA. 
271 
Isops contorta (Bowerbank). 
Pachymatisma contorta, Bowerbank, Proc. Zool. Soc. Bond., p. 327, pi. xxxi. figs. 7-11, 1873. 
Sponge. — Branching ; branches irregular, short, stout, anastomosing ; surface undu- 
lating ; oscules small, scattered ; cortex 1 *2 mm. thick. 
Spicules. — I. Megascleres. 1. Oxea, 1*838 by 0*035 mm., sometimes passing into 
a strongyloxea. 2. Ortliotrisene, rare and variable in dimensions. 
II. Microscleres. 3. Sterraster, obtusely oval, depressed, 0*16 mm. in diameter. 4. 
Somal spheraster, 0*01 mm. in diameter. 5. Choanosomal oxy aster, 0*032 mm. in 
diameter. 
Colour. — Light brown in the dried state. 
Habitat. — Fiji Islands. 
Remarhs. — Measurements were taken from a type-slide in the British Museum. The 
characteristic microstrongyles of Pachymatisma are absent in this species. 
Family II. Placospongida: (Gray). 
Sterrastrosa not possessing triaene spicules ; the only megascleres are tylostyles. The 
sterrastral layer of the cortex is subdivided into irregular or polygonal plates, which are 
connected together by fibrous tissue. 
Genus 1. Placospongia, Gray. 
Placospongia melohesioides, Gray. 
Placospongia melolesioides, Gray, Proc. Zool. Soc. Bond., pp. 127-129, woodcut, figs. 1-4, 1867. 
1 „ „ Carter, Ann. and Mag. Nat. Hist., ser. 5, vol. vi. pp. 53-55, 1880; 
vol. ix. p. 357, pi. xii. fig. 33, 1882. 
1 „ „ 0. Sch., Spong. Atlant. Gebiet., p. 72, pi. .vi. figs. 15-17, 1870. 
Sponge. — Branching ; branches angular, axis occupied by a dense accumulation of 
sterrasters. Surface even, smooth. Oscules (?). 
Spicules. — I. Megasclere. 1. Tylostyle, actine cylindro-conic, strongylate, 1*03 by 
0*014 mm., tylus 0*0178 mm. in diameter. 
II. Microscleres. 2. Sterraster, ellipsoidal, 0*071 by 0*058 mm. to 0*067 by 0*063 
mm. 3. Spheraster, centrum large, forming the greater part of the spicule, ends of the 
actines forming short tent-like spines upon it, 0*0129 mm. in diameter. 4. Micro- 
strongyle, cylindrical, entirely spined ; spines short, of unequal lengths, cylindrical, 
rounded at the ends, 0*24 by 0*008 mm. 5. Spherules, minute, 0*0012 mm. in diameter. 
