90 PORIFERA. 



Sub-order 2. HETEROCCELA. 



Calcareous sponges in which the collared cells arc confined to more or less well- 

 defined flagellated chambers. 



Fam. 1. Leucascidae. Flagellated chambers branched, opening into exhalent 

 canals which converge towards the oscula ; their outer ends covered over by a 

 dermal poriferous membrane. Skeleton of irregularly scattered radiate spicules. 

 Leucascus Dendy. 



Fam. 2. Sycettidae. The blind outer ends of the flagellated chambers pro- 

 jecting freely on the surface and not covered by a dermal cortex. Chamber 

 skeleton articulate. Sycetta H. ; Sycon Risso ; Sycantha Lendf. 



Fam. 3. Grantiidae. With poriferous dermal cortex covering the chamber 

 layer ; without subdermal sagittal triradiates. Chamber skeleton varies from 

 regularly articulate to irregxilarly scattered. Grantia Fleming; Ute O.S. ; 

 Utclla Dendy; Anamixilla Pol.; Sycyssa H. ; Leucandra H. ; Lelapia Gray; 

 Leucyssa H. 



Fam. 4. Heteropidae. With poriferous dermal cortex ; with subdermal 

 sagittal triradiates. An articulate chamber skeleton present or absent. 

 Grantessa Lendf. ; Hetcropia Carter ; Vosmceropsis Dendy. 



Fam. 5. Amphoriscidae. With poriferous dermal cortex ; conspicuous sub- 

 dermal quadriradiate spicules with inwardly directed apical rays are present. 

 Hcteropegma Pol. ; Amphoriscus H. ; Syculmis H. ; Lcucilla H. 



Class II. TRIAXONIA. 



With triaxonic (sex-radiate} spicules and large flagellated chambers. 



Order 1. HEXACTINELLIDA.* 



Sponges u-ith very loose soft parts, ami irith silicious spicules u-hich 

 are either isolated or united into a connected frameioork, and belong 

 or are reducible to the triaxial system. Canal system simple, irith 

 syconate chambers. 



In tlie Hexactinellida the ectoderm is a thin layer containing 

 nuclei, but without discernible cell outlines. The lining cells of 

 the flagellated chambers project into the cavity of the chamber, 

 and stand some distance apart from one another. Their bases are 

 connected by basal strands which are apparently processes of the 

 cells themselves. No flagella or collars have so far been detected, 

 but there can be but little doubt that they exist as in other sponges. 



The spicules contain a central canal filled with a soft granular 

 substance which is continuous with adjacent structures through 

 openings at the end of the rays. These are closed when the spicule 

 has ceased to grow. The spicules (Fig. 78) typically consist of a 

 system of three equal axes intersecting at right angles, and variations 

 in this type are due to the unequal development or branching of 



* F. E. Schulze, "Report on the Hexactinellida." Challenger Reports, 

 vol. 21, 1887. 



