6. Calcinea (Lace-chalks).
Class 5. Tetraxonida (s.sj Four-ray Sponges.
Order 7. Plakinida (Flat Four-rays).
8. Tetractinellida (Grapnel-sponges).
9. Donatiida (Plane-fruits).
[1o. Lithistida (Stony Sponges). Not a true group.] This classification represents the opinions of the writer; others will be found in the text-books. Vosmaer (i3), Sollas (2), Delage (5) and Dendy separated Calcarea from all other sponges. Dendy included all Needle-sponges in Tetraxonida. Hentschel (4) in the Phylum and Class Porifera recognises five equal Orders; Pin cushions are placed in Tetraxonida, the other Needle-sponges are united with Horny Nets in Cornacuspongida and the Horny Bushes form the 5th Order, Dendroceratida. Emile Topsent in 1928 (i7) • divides the Porifera into three Classes: Calcaria (= Chalks), Triaxonia (= Glass-sponges), and Demospongiaria to include the rest. Demospongiaria contain the Sub-classes Tetracti nellida, Monaxonellida, and Ceratellida (=Horny Sponges). Tetraxonellida are the Four-rays without the Plane-fruits and Gristly sponges : these are included in Monaxonellida (Needle sponges), and united with Pin-cushions to form the Order Hadromerina. Monaxonellida have four Orders : Hadromerina; Halichondrina (= Fans) ; Poecilosclerina (= Claw-sponges); Haplosclerina (=Spindle-sponges). The figures (except dates) in parentheses following authors' names in the foregoing and sub sequent paragraphs refer to works so numbered in the Bibliog raphy at the end of this article.
The "Glass Sponges" are exclusively deep-sea sponges, with large spicules, often extended into long threads like delicately spun glass (fig. 9), but typically four-rayed or six-rayed rec tangular crosses with one or more rays often exaggerated or suppressed. The "Needle-sponges," with spicules generally like needles, rods, or spindles, to 2 mm. long, comprise the ma jority of sponges met on the shore. "Pin-cushions" show also some fine "pinheaded" spicules generally really trefoil—or cross headed; sponges mostly massive and corky, often bun-shaped. "Claw-sponges" usually show with a good microscope minute C shaped or G-shaped spicules (often only 3 c. long), the chelae or "claws," with commonly a 3-fluked anchor or claw at each end of the C or G; the large spicules being needles, bodkins, or rods (fig. 8) (rarely spindles), and a stout bodkin with prickles on it (acantho-style) very characteristic; sponges often hand shaped, with many fingers or clustered turrets but others form flat crusts. "Fans" are typically shaped like antler-ferns with their 'Outside marketable Horny Sponges only about half-a-dozen species have popular names, and the groups are known to zoologists by Latin and Greek names, usually of six syllables. For this article the writer
has ventured to coin names in English.
branches in one plane (fig. 3) sometimes coalescing into a fan, supported by branching feathery fibres of spicules; needles, with or without spindles, are the commonest spicules, never prickly bodkins or claws, which Dendy considered were possessed ancestrally and lost (1921, "Sealark," p. III). In "Spindle-sponges" (including fresh-water sponges, "Witches' but ter" of our ancestors) all the numerous spicules have equal sym metrical ends ; ends of neighbouring spindles or rods are generally cemented together by spongin into a network or scaffolding, often rectangular (fig. I I). "Horny Sponges," the marketable kinds, grow in warm seas at 2-20 fathoms depth; in most others the spongin is too hard and brittle to be commercially useful. Inside the fibre of many "Nets" is much sand. The "Chalky Sponges," mostly small, frequent temperate shores; the microscope shows 3-ray and other spicules (fig. 12) soluble in acid. "Banana chalks" are characterised by tall chimneys, in shape like ban anas (Minchin) ; they are all white to whitish-brown, with many Y-shaped, or more accurately T-shaped or T-shaped spicules (fig. I 2) .
The "Lace-chalks" are coral-red, sulphur-yellow, snow-white and fawn colour, usually making a little crust or cushion of lace work on the rock with occasional short chimneys (fig. 7) ; their equiangular spicules have 3 rays about mm. long (fig. 12). "Four-ray Sponges" are characterised by spicules corresponding to the name. They may be symmetrical resembling the calthrops of mediaeval warfare, but usually the ray pointing inwards is of different thickness and length from the other three rays. Of the "Flat Four-rays" Plakina has minute, scattered spicules; Os carella has no spicules. The "Grapnel-sponges" show slender spicules with one long arm pointing to the centre of the sponge and three prongs, often curved ; they include, however, the "Starry-sponges" (Stellettidae), among which often no four ray spicule can be found, and which lead us on to the "Gristly sponges" (Chondvilla, Sea-kidney, stars only; Chondrosia, Gristle-sponge, no skeleton) and to the "Plane-fruit Sponges," which have a crust of stars, with needles and spindles arranged in a radiating skeleton (Donatia, fig. 2, the Common "Sea Or ange," is like a small, yellow, hard golf-ball). The deep sea "Stony Sponges" have shapeless silica laid down on their spicules, mortis ing them together like the sutures of the skull ; their relationships are uncertain ; probably they really belong to several groups, some descended from Needle-sponges.