MR. S. 0. RIDLEY ON THE GENUS DIRRHOPALUM. 483 



echinated by small acuates. A horny secondary fibre, at approxi- 

 mately right angles to them, connects the primary fibres and con- 

 tains the dumbbells, which also occur sparingly in the primaries. 



The dermal skeleton is formed of a reticulation of the dumb- 

 bell spicules lying generally in twos side by side, making angular 

 meshes, their ends united by dark material polarizing light. 



Of the slceleton-spicules : — (1) the smooth main acuate tapers 

 slightly to its base, but otherwise agrees with Mr. Carter's descrip- 

 tion ; size *475 by "0206 millim. (2) Short echinating acuate, 

 smooth ; is bent abruptly, like a scimitar, at about one third of 

 its length from the sharp point ; size '114 by "095 millim. (3) Fine 

 acuate, smooth, slightly inflated basally, scattered over fibres and 

 in dermis, probably young form of (1) ; size about '3167 by 

 •006334 millim. (4) Dumbbell, with smooth curved shaft and 

 distinct heads, very minutely microtuberculate rather than micro- 

 spined (spines made too evident in Mr. Carter's figure for the 

 scale on which it is drawn) ; heads of same diameter as middle 

 of shaft ; size '234 by *019 millim. 



Flesh-spicules. — (1) Tricurvate, as given by Mr. Carter; size 

 "07 by '0025 millim. (2) Equianchorate, navicular ; shaft nearly 

 straight ; proximal edges of palms slightly bidentate ; length 

 •019 millim. 



Obs. I had occasion to examine the specimen to settle a doubt as 

 to the identity of the species with D. novizelanicum, sp. n. (infra), 

 and so think it worth while giving these measurements and notes, 

 which supplement and slightly correct Mr. Carter's careful de- 

 scription. It differs essentially from D. novizelanicum in the 

 smoother and more finished condition of the dumbbell spicule, 

 in the proportions and shape of the smaller acuate, and in differ- 

 ences in the measurements of most of the spicules. On the 

 whole, in spite of its locality (Gulf of Manaar, Ceylon), it is not 

 far removed in structure from the Floridan species D. gymnazon. 



7. DlRRHOPALUM NOVIZELANICUM, Sp. U. (PL XXIX. figs. 8-16.) 



Branching cylindrical stems of constant diameter, viz. about 

 3 millim., having a delicate linear fucus for their axis ; the 

 branches sometimes anastomose. Apparently no rooting base ; 

 all extremities, both upper and lower, consisting of rounded points. 

 Surface velvety, set with very slightly projecting ends of spicules. 

 Texture elastic, slightly compressible. Colour in spirit dull 

 umber-brown. 



Vents. None apparent. 



