A NEW GENUS OF THE HEXACTINELLID SPONGIDA. 233 



DESCRIPTION OF THE PLATES. 

 Plate XXXVI. 



Fig. 1. Steere's Sponge {Dendrospongia Steerii). Drawn on stone from a photograph, aided by a piece 

 of the specimen itself, and reduced f nat. size. In accordance with the text the lettering 

 used signifies : — ro, root ; s, stem ; r, right, m, middle, and I, left main hranches ; b, secondary 

 branch; /, fork. 



Fig. 2. Portion of a terminally forking branch, of the natural dimension, w, whorl or spiral tuft ; br, 

 interlocking branch of same; g, intervening groove or spiral depression between the tufts. 



Fig. 3. A small segment of a branch of Dendrospongia at one of the spiral grooves. Enlarged about 

 twice nat. size. This shows the appearance of the veil or delicate latticework of square 

 meshed spicules, spread over the surface and partially extending to the raised whorls ; openings 

 of the oscula or vents are seen beneath the veil. 



Fig. 4. Fragment of the interior of a branch, illustrating mode of skeletal arrangement of the large glassy 

 fibres. Enlarged about twice nat. size. 



Plate XXXVII. 



Fig. 5. Sketch of the foreshortened summit of a branch, exhibiting termination of spines &c. Of 

 nat. size. 



Fig. 6. A transverse section (somewhat enlarged) of the stem at the base of one of the branches, and where 

 the ruff or whorled spicula have been considerably rubbed away. The central framework has 

 many irregularly contoured canals and of different sizes; towards and at the peripheral margin 

 the glassy fibres appear to radiate, the most marked of which constitute what remains of 

 the abraded whorls. 



Fig. 7. Another cross-section made higher up, and where branching occurs ; hence its more compressed 

 oval form, also in part due to the exterior spicula being worn off. Nat. size. 



Fig. 8. A median longitudinal section of part of a rubbed branch of D. Steerii, and where only indications 

 of the spicular whorls are present. Enlarged about once and a half nat. size. This illustrates 

 the exact disposition of the internal main body of the glassy fibres or basal structure of the sponge.. 

 The long, large, strong, and vertically directed bundles of spicula incline outwards or with 

 slightly sinuous curve follow a certain spiral arrangement, the marginal elevations cor- 

 responding to the whorls and the depressions to the grooves. A network of short cross or 

 oblique spicula bind together the axial and longitudinally directed stouter sorts. Canals and 

 oscula permeate freely. 



Fig. 9. A greatly magnified representation of a portion of the framework or glassy fibre as seen on its 

 superficial aspect. It exhibits in position the so-called veil-layer or lattice-like squares of the 

 dermal hexactinellid spicula (see fig. 23, a, b), also here and there deep-seated hazy patches of 

 the fiesh-spicula &c. 



Fig. 10. Another portion of the glassy fibre, from the interior, still further enlai'ged, the dotting showing 

 its spiny roughening. At a one of the larger rectangular interspaces between the reticulated 

 vitreous spined fibre is partly shown ; b is within a similar small circular area ; c indicates a 

 thin spined spicule, so bent and united at tips as to form a complete circle ; springing from its 

 middle is a still more delicate needle-shaped spicule (d), which lies across c; below is a mass 

 of the common fibre variously agglutinated. 



