APHROCALLISTES FEOM THE DEEP SEA. 327 



suddenly diminishing, and then being prolonged in a fine cylin- 

 drical spine (Plate XXV. fig. 17); (3) very fine cylindrical spines, 

 as slender as the long attenuate spicula, lying on the skeleton, and 

 long enough to cross a space between the meshes ; (4) short, 

 cylindrical, slender-stemmed, club-topped, spinulose projections, 

 and some of greater length (Plate XXV. fig. 18). At the base 

 of the body, however, the reticulation is of a very different 

 character to that seen elsewhere ; it is smaller, closer, and consists 

 of a vast number of hexactinellid spicules turned into skeletal 

 tissue by exogenous increase of silica. The arrangement is con- 

 tinuous ; but there are no wide interspaces. Long spicula are 

 seen here and there, cylindrical and attenuate. 



At the free growing edge, the skeleton of the body is in 

 a most rudimentary state ; and it is evident that two sets of 

 spicula are forming the lattice-work — hexactinehids and quinque- 

 radiates. But there is a very irregular broken net-looking mesh 

 of siliceous fibres, in which the shape of the ordinary spicule is not 

 traced. This irregular structure covers much space, has a derm 

 on it in some places ; and it appears to have been produced by 

 the sarcode, and not through the intervention of joining spicula 

 (Plate XXV. fig. 19). 



Here and there long, very tapering, attenuate spicula, more or 

 less closely spinuled, or rather serrated, are in contact with the 

 skeleton of the meshes (Plate XXV. fig. 16) ; and they are 

 in contact with others which are not spinuled ; and both sets 

 overlap, and form a structure between the derm and the 

 skeleton. 



The meshes of the body-skeleton are moderately uniform in 

 thickness in some parts, and the spaces between the interspaces 

 are wide, on the whole, in the stem of the sponge. The skeleton of 

 the mesh is very reticulate, and unequal in size, and usually the sur- 

 face of the large continuous spicula is granular. The spiniform 

 projections are numerous, and many cross nearly or quite over an 

 interspace. The resemblance of the skeleton to that of Aphrocal- 

 lisies Bocagei, Wright, is considerable in some parts ; but it is 

 interesting to note the structure of the base and the variety of 

 the spicule elements, as affording distinctions of more or less 

 value. 



Oscar Schmidt, in his ' Spongien der Meerbusen von Mexico ' 

 (Jena, 1880), names a form which is by no means unlike that 

 now under consideration in shape ; but even the very short 



