PORIFERA. 221 



strata. Hence palaeontology affords us no facts for determining- the 

 phylogenetic development of the Porifera, 



CLASS I. SPONGIA. 

 (With the characteristics of the Group). 



Order 1 . MYXOSPONGIA (gelatinous sponges). Soft, fleshy sponges, 

 without any skeleton, with a hyaline gelatinous mesoderru, often 

 containing fibrous cords. The ectoderm cells are fairly elongated, 

 and bear flagella. 



Fam. Halisarcidae. Jfiilixni-ca Duj. H. lolndurixO. S., colour dark violet; 

 encrusts stones; Sebenico. H. Diijurdinil Johnst., forms a white encrustmeut on 

 the Laminaria of the North Sea. 



Order 1. CERAOSPONGIA (horny sponges). For the most part 

 branched or massive sponge stocks, with a framework of horny 

 fibres, in which grains of silex and sand are present as foreign 

 bodies. 



Fam. Spongiadae. Enxponi/ia O. S., with very elastic fibrous framework, of 

 equal strength throughout, mostly capable of being used for bath and washing- 

 sponges. E. (idriitttfa 0. S., ryuhi/i O. S., zimocca 0. S., in the Greek Archi- 

 pelago, nuilixxinM O. S.. Levantine sponge, cup-shaped. $p)ujclia i-h-ijtinx 

 Nardo. 



Order 3. HALICHONDRI.E (siliciceratous sponges). Sponges of 

 very various shapes, with usually uniaxal silicious needles, simple 

 silicious spicula, which are connected by delicate or firmer plasmatic 

 structures, disposed in networks or enclosed in sponge fibres. Of 

 the numerous families the following may be mentioned : 



Fam. Chrondrosidae. {(rHmmmere'), Coriaceous sponges. Chrondrosia rcni- 

 for-mix Nardo. 



Fam. Suberitidae. Sponges of massive form, with knobbed silex spicules, 

 which, as a rule, are arranged in network. Suberlti's Mardo. <S'. donnntt-ulti 

 Nardo. Adriatic, Mediterranean. 



Fam. Spongillidae. Massive or branched with simple spicules, connected by 

 investments of sarcode. Spongilla fluviatilis Lk., Sp. lacustris Lk. 



Order 4. HYALOSPONGIA. Sponges with a firm, often hyaline 

 lattice-work of silex spicules, which present the most perfect form of 

 six-rayed spicules (Hexactmellidce), and may be cemented together 

 by a stratified silicious substance. 



Fam. Hexactinellidae (glassy sponges). AVith connected silicious framework 

 and network of stratified silicious fibres, which join the six-rayed silicious 

 bodies, frequently with isolated spicules and tufts of silex hairs, which serve to 

 attach the sponge. They live for the most part at considerable depths, and are 

 allied to the fossil Ventriculiti<l<c. Dacti/loi-nh/jc Bbk. EitplrrtcUa Owen 



