350 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [ May 13, 
Fig. 3. One of the inhalant areas on the external surface of the rigid skeleton of 
J. beatriz, exhibiting the elongo-conical defensive fibres and numerous 
verticillately spined retentive spicula im situ, x 108 linear. 
Fig. 4. One of the large excurrent orifices on the side of the great cloacal cavity 
within the sponge of L, beatrix, x 108 linear, 
PuatEe XXII. 
Fig. 1. A small portion of the rigid skeleton of Zphiteon panicea from Porto 
Rico, exhibiting the abundance of the gemmules in some parts of the 
sponge, X 108 linear, 
Fig. 2. A portion of one of the fibres forming the oscular area of [phiteon 
beatrix, exhibiting the compound reticulate nature of its structure and 
a few of the slender acerate spicula iz situ, X 108 linear. 
Fig. 3. One of the attenuated rectangulated hexradiate interstitial spicula with 
one of the shaft-radii spinous, from Z. beatriv, < 308 linear. 
Fig. 4. A retentive verticillately spined spiculum from Z. beatriv, 308 linear. 
Figs. 5, 6, 7, 8. Four of the porrecto-multiradiate retentive spicula from Z. bea- 
trix, 308 linear. 
Fig. 9. One of the subfusiformi-cylindrical entirely spinous spicula from J, 
beatriz, X108 linear. 
Fig. 10. A portion of the surface of the rigid skeleton of Iphiteon subglobosa, ex- 
hibiting the umbonal clusters of coarse tubercles, rectangulated hex- 
radiate interstitial spicula 7 situ, and numerous spinulo-quadrifur- 
cate and pentafurcate hexradiate stellate retentive spicula dispersed 
amidst the interstices of the skeleton, x 108 linear. 
Fig. 11. One of the minute spiculated biternate retentive spicula of the dermal 
membrane of J. subglobosa, x 666 linear. 
Fig. 12. Two of the rectangulated hexradiate auxiliary fibres from I. subglobosa, 
based on a portion of a fibre of the rigid skeleton, anastomosing by 
their radii, X 175 linear. 
Fig. 13, One of the pentafurcate hexradiate stellate retentive spicula of 1. subglo- 
bosa, X 666 linear. 
Puiate XXIII. 
Fig.1. A small portion of the surface of the rigid skeleton of Zphiteon Ingalli, 
exhibiting its confluent rotulate structure with quadrifurcate hexra- 
diate stellate spicula amidst the fibres opposite a, a, a, a, X 108 linear. 
Fig. 2. One of the quadrifurcate hexradiate stellate retentive spicula of Z. Ingalli; 
three of the primary radii having been broken off, the quadrifurcate 
structure of the remaining radii is very distinctly displayed: x 530 
linear. 
Fig. 8. One of the rectangulated hexradiate interstitial spicula of L Ingalli, x 
108 linear. 
Fig. 4. A small portion of the surface of the rigid skeleton of J. callocyathes, 
exhibiting the more or less verticillate disposition of the minute spines 
of the skeleton-fibre, x 108 linear. 
Fig. 5. One of the rectangulated hexradiate interstitial spicula of Z. callocyathes, 
f 175 linear. 
Fig. 6. A furcated foliato-expando ternate connecting spiculum of J. callocya- 
thes, covered by the minute, short, stout acerate tension-spicula of the 
dermal membrane, x 183 linear. 
Fig. 7. A very perfect and beautiful example of a spinulo-multifureate hexra- 
diate stellate retentive spiculum of J. callocyathes, x 666 linear. 
Fig. 8. A view of portions of two of the intervening planes of perforated sili- 
ceous tissue parallel with the external surface of the rigid skeleton, 
and which divide the layers of crypt-like tissue of the skeleton of 
Myliusia Grayii from each other, with their numerous circular orifices 
of intercommunication between the upper and lower strata of the 
skeleton, X 108 linear. 
