ERYLUS CALICULATUS. 311 



Tlie colour of the sponge (in spirit) is dirty white. 



The suj^erficial jjart of the Ijody is differentiated to form a coHex which con- 

 tains an aspidaster-armour and is about 65 ft thick. 



Canal-system. The, probably efferent, apertures on the depressed, terminal 

 face of the sponge are surrounded by sphincter-membranes. The flagellate 

 chambers (Plate 6, figs. 28, 29) are more or less spherical and 1.5-22 ji in diam- 

 eter. 



The skdelon consists of rhabd megascleres, microrhabds, triaenes, acanth- 

 tylasters, slender-rayed oxyasters, small oxysphaerasters, and aspidasters. 

 Some of tlie rhabd megascleres form bundles (Plate 6, fig. 26a), others are iso- 

 lated and scattered. The bundles extend from the base upward and outward; 

 on nearing the surface they curve, where necessary, so as to abut steeply or 

 vertically on the cortex. The dadomes of the triaenes extend paratangentially 

 just below the cortical armour, their rhabdomes being directed radially inwards. 

 The triaenes occupy the interporal spaces (Plate 6, fig. 23) and often form well- 

 defined groups at the intersections of the interporal zones. The microrhabds 

 form a thin superficial layer overlying the aspidaster-armour and occuj^y the 

 mantles surrounding the cortical canals, chiefly their outer parts farthest from 

 the lumen. A few microrhabds are also found scattered in the choanosome. 

 The acanthtj'lasters and the slender-rayed oxyasters, which latter I consider as 

 young acanthtylasters, are numerous in all parts of the choanosome and extend 

 right up to the cortex and even into the mantles of the cortical canals. The 

 small oxysphaerasters are confined to the subcortical region and the mantles 

 of the cortical canals, on the inner surface of which they are often cjuite numer- 

 ous. The asjiidasters occupy the proximal and middle parts of the cortical 

 armour in dense masses, leaving only the mantles of the cortical canals free. 

 Some as{3idasters also occur scattered in the choanosome. The aspidasters in 

 the armour are mostly situated paratangentially. Next the mantles of the 

 cortical canals, however, they often assume other positions. 



Most of the rhahd megascleres (Plate 6, figs. 24, 25) are very blunt amphi- 

 oxes (Plate 6, figs. 24a, 25a), many indeed so blunt that they can be considered 

 as ampliistrongyles. A few blunt styles (Plate 5, fig. 24c) and branched rhabd, 

 derivates have also been observed. Most of the rhabds are more or less curved, 

 usually more strongly in their central part than at their ends. The rhabds are 

 410-850 /I long and 10-19 /t thick, the average measurements of the three 

 longest and thickest being 723 by 18 /l/. 



The mia-orhabds (Plate 6, figs. 1, 2, 4a, 5a; Plate 7, figs. 74a, 77a, 78, 80) 



