CALCAREA 261 



Genus Leucettusa, Haeckel 



Leucettusa haeckeliana (Polejaeff). 



Leucetta haeckeliana, Polejaeff, 1883, p. 69, pi. ii, fig. 6, pi. viii, figs. 1-6 ; Leucettusa haeckeliana, 

 Dendy and Row, 1913, p. 739. 



Occurrence. St. WS 84: Falkland Islands, 75-74 m.; St. WS 243: Falkland Islands, 144-141 m. 



Distribution. Kerguelen. 



Leucettusa simplicissima, sp.n. (Plate XL VIII, fig. 3). 



Holotype. B.M. 28. 2. 15. 35. 



Occurrence. St. WS 84 : Falkland Islands, 75-74 m. 



Diagnosis. Sponge tubular ; skeleton of chamber layer composed of triradiates and 

 quadriradiates of fairly constant size; cortical skeleton composed of a dense mass of 

 large triradiates; without special gastral skeleton. 



Remarks. The species is represented by a quantity of branching tubes, each one 

 being cylindrical and slightly flattened, with a single apical oscule. The tubes appear to 

 have grown erect but now there is nothing to show their method of attachment. The 

 largest are 3 cm. high and 7 mm. in diameter. There is no oscular fringe. The cortical 

 and medullary layers are well marked, the latter being the thicker. The flagellated 

 chambers are elongate, reaching from the gastral surface to just beneath the dermal 

 cortex. 



The chamber layer contains small triradiates and quadriradiates of fairly constant size 

 scattered sparsely between the chambers. These are of the normal type and the rays of 

 a typical example measure 0-036 by o-oo6 mm. Occasionally these spicules may suff'er 

 reduction to two rays. 



The cortical skeleton consists of a mass of large irregularly placed triradiates of fairly 

 constant size, several layers thick, the rays of which may reach as much as 0-21 mm. in 

 length and o-oi8 mm. in thickness. 



There is no special gastral skeleton, although occasionally triradiates similar in all 

 respects to those of the chamber layer may be found lying tangentially in the wall of 

 the gastral cavity. 



The characteristic feature of this species is the simplicity of its skeleton, and in this 

 it diflFers markedly from all the known species of Leucettusa. If anything is to be said of 

 its relations to other species it is that L. simplicissima is more nearly like L. tubulosa, 

 Dendy, from New Zealand, in external form, but approaches L. haeckeliana (Polejaeff), 

 from Kerguelen in spiculation. In fact, it differs from the latter mainly in the absence 

 of the large quadriradiates. 



