Sponges from the Atlantic Ocean. 239 



discoloration, when placed under the microscope, is found to 

 arise from the presence of sarcode charged with two kinds of 

 spicules, viz. one skeleton- and one flesh-spicule. Skeleton- 

 spicule acuate, straight, but with the large end suddenly bent 

 to one side (like the head of a walking-stick), and terminating 

 attenuatinglj in a point at the other end, sparsely covered 

 with short vertical spines throughout, 80- by 3-6000ths inch 

 (PI. XV. fig. 43, a). Flesh-spicule a simple bihamate, much 

 curved, and more or less tortuous (fig. 43, h). The skeleton- 

 spicules are sparsely imbedded among the flesh-spicules, which 

 are exceedingly numerous and thrown together confusedly, so 

 as to form the greater part of the mass (fig. 43, c). Pores 

 and vents not seen. Size of portion of discoloration in the 

 Corallistes about 5 inch in diameter. 



Hah. Marine, on Corallistes Boioerhankii. 



Log. Station 25, in 374 fathoms, near Cape St. Vincent. 



Ohs. This sponge is chiefly remarkable for the form of its 

 skeleton-spicule and the mass of bihamates in which it is 

 imbedded. Being parasitic among the spicules of Corallistes, 

 I, of course, can give no description of its form : I am not 

 quite certain that it should be called a Microcionaj and there- 

 fore only give this generic name provisionally. 



Microciona pusilla, n. sp. (PI. XVI. fig. 51, a, 5, c, d.) 



I have met with another Microciona of the same kind, 

 growing on Polytrema utriculare^ not dredged up on board 

 the 'Porcupine' (Ann. 1876, vol. xvii. p. 210), but probably 

 from the tropics. (Dr. Bowerbank has figured a similar 

 spicule from Oculina rosea, op. cit. vol. i. pi. xi. fig. 243.) In 

 my instance, however, the skeleton-spicules are smooth, and 

 the bent portion of the large end has a tendency to a spiral 

 twist (a, h) ; while they grow erect on the surface of the 

 Polytrema, with fine acuates between them (c), and minute 

 bihamates (?) scattered throughout the structure, which are 

 almost too small to be satisfactorily described under a 5-inch 

 object-glass [d). The thick skeleton-spicule with bent large 

 end is hardly more than a quarter the size of that of Microciona 

 intexta, although somewhat similar in form, being about 36- 

 by l-6000ths inch in its greatest diameters. 



PhahelUa ventilabrum, Tih., = Halichondria v., Johnston. 



Fragments of this sponge appear in jars 61-63, 64, 65, and 

 84, which, being the numbers of the stations where they were 

 dredged up, indicate a depth varying between 155 and 640 

 fathoms, and a locality extending north of the Butt of Lewis to 



