452 COLLECTIONS FROM MELANESIA. 



fibre. (4) Equianchorate ; navicular, shaft almost straight, pointed 

 at each end ; length -01G--018 millim. 



Hab. Port Darwin, 7-12 fms. ; bottom sand, mud, and shells. 



The above diagnosis is based on a large specimen. A small 

 specimen (which is perhaps the apex of a larger one), 36 millim. 

 high, also occurs from the same place and same depth, differing 

 from it in having no perceptible horny fibre, in being, in consequence, 

 soft and flaccid, and in having the spined acuate confined to a 

 central axis which contains a large quantity of sand ; it is probably 

 identical with the large specimen, its differences being partly in- 

 dividual, partly due to youth ; it contains the parasite Spongio- 

 phar/Ks, Carter. This very fine species appears to be referable to 

 Rhapliidophlus by possessing a distinct dermal crust composed mainly 

 of smooth spinulate spicules with their points projected outwards, 

 but adds to this the presence in this crust of the spined echinating 

 spicules, a feature in which it resembles Dirrhopalum. The crust 

 is thin, but appears to represent the correspondingly situated struc- 

 ture in R. cratitius, Esper (Ehlers). Its root-like base recalls the 

 horizontal meshwork figured by Esper, and here, as there, the erect 

 portion appears to have no real tendency to form branches ; but, 

 besides the differences in the dermis, the skeleton and echinating 

 spicules are both much longer than in the type and hitherto only 

 recognized species of the genus. The height of the perfect and 

 well-preserved spirit-specimen is 470 millim. (1S§ inches). The 

 arborescent form, the strongly horny fibre, the slenderncss of the 

 skeletal and echinating spicules, the replacement of the spinulate 

 for the most part by the spined acuate in the main-skeleton fibre, 

 and the thickness of the dermal crust, distinguish R. arborescens from 

 R. procerus. 



81. Rhapliidophlus, sp. 



The following appears to be distinct from all known species of 

 the genus, but more material is necessary for full description : — 



A small dry specimen of subramose cylindrical growth, 45 millim. 

 long by 12 millim. in greatest diameter, the surface proliferating 

 into ridges and processes 2-3 millim. high, giving it a flocculent 

 appearance. Colour pale dusky brown. Skeleton irregularly rect- 

 angular in arrangement ; spicules united in the fibre by a small 

 amount of very pale horny substance, which is only occasionally 

 seen outside the spicules ; primary fibres about 8 to 10, secondary 

 6 to 8 spicules broad. Dermal skeleton a single layer of smooth 

 subspinulates in tufts radiating outwards. 



Spicules : — (1) Smooth acuate, tapering gradually to sharp point; 

 size -23 by -0095 to -0127 millim. : in fibre. (2) Smooth sub- 

 spinulate, forming dermal layer ; head very slight, larger than shaft : 

 tapering gradually to sharp point ; size *25 by "0095 to "0127 millim. 

 (3) Spined cylindrical, tapering gradually from well-rounded, very 

 slightly dilated base to rounded apex, which is about one third 

 the diameter of the base ; spines prominent, sharp, distal ones 



