ERYLUS OXYASTER. 



269 



extend radially from the base of the sponge to the cortex and abut vertically on 

 the latter. The microrhabds occupy in dense masses the outer layer of tlie 

 cortex. The superficial ones are situated paratangentially, the deeper ones 

 mostly obliquely or radially. The teloclades are mostly regular dichotriaenes, 

 but some irregular dichotriaene-derivates and simple plagiotriaenes have also 

 been observed. The cladomes of these teloclades extend paratangentially; just 

 below the cortex their rhabdomes arc directed radially inward. The oxyasters 

 form a series from small many-rayed to large few-rayed ones. As, however, the 

 asters of medium diameter and ray-number are not nearly so numerous as the 

 large few-rayed and small many-rayed ones, this series does not appear uniform 

 and large few-rayed and small many-rayed oxyasters can readily be distin- 

 guished. The large few-rayed oxyasters are quite uniformly scattered through- 

 out the choanosome; the small many-rayed ones on the other hand, although 

 also present in all parts of the choanosome, are much m(jre numerous in the 

 subcortical region, particularly in the roofs of the subcortical cavities and the 

 walls of the cortical canals, than elsewhere. The aspidasters, which occupy 

 the inner layer of the cortex, are rather irregularly arranged. They exhibit 

 hardly a trace of a paratangeritial orientation. 



The regular amphioxes (Plate 4, figs. 6-9) are isoactine, gradually attenuated 

 towards the ends, and usually rather sharply pointed (Plate 4, figs. 6-8), more 

 rarely blunt (Plate 4, fig. 9). They are straight (Plate 4, fig. 6) or slightly and 

 uniformly curved (Plate 4, figs. 7, 9), exceptionally abruptly bent in the middle 

 (Plate 4, fig. 8). The amphioxes are 1.8-2.9 mm. long and 60-85 ft thick. 



The rare styles (Plate 4, figs. 10, 11) are slightly curved, simply rounded 

 off at one end and gradually attenuated towards the other, which is usually 

 very blunt. They are 1.9-2.3 mm. long and 60-105 pt thick. 



The irregular derivates of the rhabd megascleres (Plate 4, figs. 12-19) have 

 similar dimensions to the regular rhabds. They appear as more or less curved 

 amphioxes, either strongly angularly bent near one end, or provided with one 

 or more branches. The angle in the angularly bent forms (Plate 4, figs. 12 13) 

 is 15-95°. The branched forms bear one (Plate 4, fig. 15) or, more frequently, 

 two (Plate 4, figs. 16, 19) or three branches (Plate 4, figs. 17, 18), which arise 

 either from the same part (Plate 4, figs. 16, 19) or from different parts of the 

 shaft (Plate 4, figs. 17, 18). The branches are always very much shorter than 

 the shaft, rarely over 400 /i long, straight, conical, and terminally either pointed 

 (Plate 4, figs. 16, 17, 18 the upper right one, 19) or rounded (Plate 4, figs. 15, 18 

 the upper left and the lower one). The angle at which they arise is very vari- 



