78 CCELENTERATA 



H. longissimum Verrill. Leugtli 40 cm. : in 00 to 95 fathoms off the 

 New England coast. 



Class 3. DEMOSPONGIAE. 



Usually massive and often brightly colored sponges with thick walls 

 and small round flagellate chambers connected by branched exhalent 

 canals with the cloaca! cavity; spicules vei'y varied in form, being often 

 monaxonic and straight and needle-like, or tetraxonic with 4 crossed axes, 

 giving them 8 rays; spongin either present with the spicules or not, or 

 the fibres alone may be present or both be wanting : 4 orders. 



Key to the orders of Demospongiae : 



Oi Skeleton formed of tetraxonic silicious spicules of a variety of forms without 

 needle-like spicules and without spongin ; in rare cases no skeleton. 



1. Tetractinellida 



Oi Skeleton of needle-like spicules with often others and with or without spongin 

 fibres 2. Monactinellida 



O3 Skeleton of spongin fibres alone 3. Ceraospongiae 



Ot Skeleton entirely wanting 4. Myxospongiae 



Order 1. TETRACTINELLIDA.* 



Sponges with usually a hard outside crust or cortex containing 

 megascleres which form the principal framework of the body, micro- 

 scleres occurring throughout the mesoglea and being of a variety of 

 forms, but usually reducible to the tetraxonic type : 8 families and over 

 325 species. 



Family 1. THENEIDAE. 



Body usually more or less mushroom-shaped with the osculum in the 

 center : 1 genus. 



Thenea Gray. With the characters of the family: several species. 



T. echinata Verrill. Body 5 to 10 cm. broad and not quite so high, 

 with a short, thick stalk; upper portion with radiating bundles of spicules 

 which project beyond the surface : New England coast north of Cape Cod. 



Family 2. GEODIIDAE. 



Body globose with a thick crust, provided with masses of spherical 

 spicules: about 8 genera and 180 species. 



Geodia Lamarck. Tetraxonic needles radially arranged and con- 

 fined to the periphery; oscula sieve-like, in groups; incurrent openings 

 also sieve-like and scattered : 70 species. 



G. miilleri (Fleming). Spherical or flattened in youth, later irregu- 

 larly lobed; diameter and thickness sometimes 30 cm.: cosmopolitan; 

 Jamaica; West Indies. 



* See "Totraxonia," by R. von Lendenfeld, Das Ticrreich, 1903. 



