612 coLijionoifs peom the wbstees htdian oceah. 



ECTTONID^. 



Two of the six species obtained, viz. Clathria frondifera and 

 Acarnus ternatits, must now be regarded as characteristic of the 

 equatorial parts of the Indian Ocean. As this ocean appears to be 

 the main focus of Glaihria, it is not surprising to find this most 

 prolific genus further represented here by two new species. 



CLATHEIA. 



The three species found in this district contrast, by their decum- 

 bent or incrusting habit, with the fine arborescent species which 

 prevail in Australia. 



34. Clathria frondifera, Bowerbank. (Piatb HII. fig. J.) 



See Part I., p. 448, of this Report. 



This species seems to be almost as abundant in this region as in 

 the J\[orth- Australian seas. The specimens agree well, both as to 

 outward form and size and in their fibre-characters, with those 

 described by me (Part I. p. 448) from those seas. The only diver- 

 gent points which they present are found in the spiculation, viz, 

 the slightly greater diameter attained by the smooth deep-skeleton 

 acuate in some of the specimens, and the wide range of dimensions 

 exhibited by this spicule : it ranges from -16 to "25 millim. in 

 length and from -008 to "0127 millim. in thickness ; the latter 

 thickness is not reached by the Australian specimens, but is exhi- . 

 bited by one from Caspar Strait, and exceeded (-0158 miUim.) by 

 the type specimen, from the Straits of Malacca. 



Hab. Providence Eeef and Island, Masearene group; Amiraute 

 Islands ; SeycheUe Islands ; 12-24 fms. 



35. Clathria decumbens. (Plate Lin.~ fig. K; Plate LIY. 



fig8.gr,g,'.) 



Sponge massive, sessile ; forming low, spreading masses, either 

 (a) of submonticular form, i. e. highest in the middle and terminating 

 laterally in a few short angular ends, or (b) commencing as a hori- 

 zontal flattened cylinder, sessile by its lower side, terminated at each 

 end by rounded (sometimes free) extremities, and sometimes sending 

 off lateral lobes of similar character. Surface (in uhmacerated 

 condition) slightly undulating, either (in 6) glabrous, formed by a 

 parchment-like brown membrane which conceals the honeycombed 

 main mass of the sponge, or (in a) much grooved, having a worm- 

 eaten appearance, the surface between the grooves slightly and 

 minutely pilose \dth the ends of the skeleton-fibres, the bottom of 

 the grooves themselves smooth, membranous. Vents moderately 

 abundant (7 or 8 in small specimen), scattered on all parts, round, 

 suborbicular, or oval ; opening level with surface ; provided with 

 thin membranous margins ; diameter 1-4 mUlim. 



Main mass of sponge composed of suboylindrical trabeculse, 6 to 



