SIDONOPS OXYASTRA. 43 



numerous small oxyasters and oxysphaerasters, numerous minute dermal rhabds, 

 and a few small anaclades. The small oxyasters and oxysphaerasters form a 

 dense coating at the surface. The minute dermal rhabds and anaclades traverse 

 the dermal layer more or less radially. Their proximal ends are implanted in 

 the distal part of the sterraster-armour layer, and their distal ends protrude 

 freely beyond the surface. The dermal rhabds are styles with attenuated, 

 proximally situated, rounded ends. In the efferent areas of the surface (Plate 6, 

 fig. 21) these spicules form dense masses. In the afferent areas they are not 

 nearly so numerous. The freely protmding ends of these spicules are in the 

 efferent areas very close together and nearly parallel, like grass on a good lawn. 

 In the afferent areas they form tuft-like groups of diverging spicules like grass on 

 arid ground. The anaclades are confined to the afferent areas. In one 

 place (Plate 6, fig. 23) I found them in great numbers. Generally they are 

 scarce. Where the monaxonid sponge-crusts, above mentioned, extend, these 

 spicules penetrate it, their cladomes lying within the attached sponge-crust 

 (Plate 6, figs. 19b, 20b), anchoring it to the Sidonops. These anaclades are 

 mostly anatriaenes, but anadiaenes, anamonaenes, and mesanaclades, chiefly 

 mesanatriaenes, also occur. 



The large choanosomal amphioxes (Plate 6, fig. 14; Plate 8, figs. 4a, 5) are 

 straight or slightly curved, 1.1 1.55 mm. long and 10-32 /i thick. 



The rare large amphistrongyles are straight, isoactine, and 0.8-1 mm. long. 

 They are in the middle 18-23 /( thick and taper towards the two equal, rounded 

 ends. The degree of attenuation is variable, as the following three measure- 

 ments show. 



Thickness in the middle Thickness at the ends 



23 n 21 fi 



20 /« 17 fi 



18 ti 12 /t 



The very rare large styles are straight and shorter and, at the rounded end, 

 thicker than the amphioxes and amphistrongyles. One that I measured was 

 850 fi long and, at the rounded end, 38 fi thick. 



The minute dermal styles (Plate 6, figs. 21, 22) are more or less, sometimes 

 rather abruptly, curved, 130-230 /(, usually about 200 ,« long, and, at the thickest 

 point, which lies between the middle and the rounded end, 3-5.5 /( thick. They 

 taper towards both ends; the distal end is sharp pointed; the proximal end 

 rounded and 1.5-3 /^ thick, usually a little less than half as thick as the spicule at 

 its thickest point. 



