of the National Antarctic Expedition. 285 



hispid under a lens. Witli several annall scattered oscules, 

 about 1 mm. in diameter, level with the surface. Flagellated 

 chambers aphodal, oval, 31 X 21 /x. 



SkeUton formed of long longitudinal lines of spicule-fibres 

 about 100 /u, thick, not forming a definite central axis, 

 radiating out in plumose manner to the surface ; witli a few- 

 isolated spicules' arranged in a scalariform manner at right 

 angles to main fibres. Spongin not perceptible. 



Spicules. — Megascleres : oxeas, 452xl9"5yLt, curved at 

 centre, attenuating gradually to sliarj) jjoints slightly planed 

 away on inner aspect. Microsclcres : canonoclielai, somewhat 

 shuttle-shaped, 45*5 /i long by 22'75/a broad, with the two 

 teeth fused to form a bridge, and witii a semicircular lamella 

 passing upwards from the shaft and downwards from the 

 dental bridge, both lamelire being nearly on the same plane 

 and nearly meeting, the lamcllaj sometimes with basal 

 tubercles. Dcveloi)ment.al forms in shape of thin, oval, 

 linear bodies, the oval at first not being complete. 



The unique specimen representing the new genus and 

 species is 12'5 cm. long and 1 cm. in breadth at the centrt-. 

 The body attenuates to fine ends, and apparently has nut 

 been attached to anything. 



The remarkable canonochelse recall to mind the sphaeran- 

 cor^ of Melonanchora, but the latter spicules have three pairs 

 of fused teeth. 



I'he canonochela3 are scattered about in tlie choanosomc in 

 considerable numbers. The shape may be compared with 

 an oval basin with the bottom cut out, and with two semi- 

 circular lids or lamellse passing horizjntally from the upjier 

 edge of the basin, so as to nearly meet ; further, it is 

 necessary to imagine such a basin turned up on its side. 



'I'he earliest developmental forms have an elongated 

 C-shape ; then the open C becomes a closed oval ; by this 

 time tlie falx at each end is perceptible, and the beginnings 

 of the lamellse appear. A iurther change leads to a marked 

 asymmetry, the thin oval ring becoming a broad band by 

 widening in a direction away from the edges whence the 

 lamelUe arise. 



Locality. Winter Quarters, l.'iO fath. 



IIOPLAKITHAKA *, gen. UOV. 



Mycalinie possessing exotyles with large spherical spincd 

 heads and with linibriatcd j)lacocheles. 



* oTrXfi ( !>!. of on^Xot ), anuouv ; KiOi^)a, n iruitai-. 



