GEODIA JAPOXICA. 73 



The sterraster-armour layer of the cortex is a little over 0.5 mm. thick. 

 SoUas gives the thickness of the cortex as 0.8 mm., Thiele the thickness of the 

 sterraster-armour layer as 0.3 mm. According to my measurement it is in 

 Sollas's type about 0.65 mm. thick. 



Skeleton. In the interior of the choanosome numerous large, stout amphi- 

 oxes are found, also less numerous large, slender amphioxes, a few large styles, 

 numerous large oxyasters, numerous small strongj-losphaerasters, and very 

 few sterrasters. In the superficial (subcortical) part of the choanosome the 

 same three kinds of large choanosomal rhabds, numerous orthotriaenes, a few 

 plagiotriaenes, many large anatriaenes, various promesoclades, numerous 

 minute dermal amphioxes, a few minute dermal styles and minute dermal ana- 

 clades, some large oxyasters, and a good many large oxysphaerasters and small 

 strongylosphaerasters occur. In this region the large rhabds and the rhabdomes 

 of the large telo- and mesoclades form radial bundles. The minute dermal 

 amphioxes, styles, and anaclades are situated radially or obliquely, and scattered; 

 the asters chiefly occupy the canal-walls. The sterraster-armour of the cortex 

 is composed of dense masses of sterrasters. Where the surface has not been 

 rubbed off or otherwise injured numerous minute amphioxes and some minute 

 dermal styles and minute dermal anaclades, implanted in the distal part of the 

 sterraster-armour, and an outer covering of small strongylosphaerasters are 

 observed. Large spicules situated radially and broken oE distally also occur 

 occasionally in this region. These are probably rhabdomes of mesoclades and 

 perhaps also of large anatriaenes similar to the ones found intact in the subcor- 

 tical layer. The spicule-fur is composed of anatriaenes and mesoproclades. 

 The Isirge slender amphioxes, the large styles, the mesoproclades, the minute 

 dermal styles, and the minute dermal anaclades are not mentioned either by 

 Sollas or by Thiele. The latter also failed to find any large oxysphaerasters but, 

 on the other hand, observed sphaeres, which were not found in the specimens 

 examined by Sollas and by myself. In the tj-pe of Sollas reexamined by me, 

 some large styles and a good many minute dermal rhabds with one end very 

 blunt and more or less style in character were met with. Mesoproclades and 

 minute dermal anaclades appear, however, to be absent. 



The large stout amphioxes (Plate 37, figs. 18-21, 22a) are generally simple, 

 straight or shghtly curved, and rather abruptly pointed. They are 2.4-3.2 mm. 

 long and 30-51 fi thick. According to Sollas they measure 2.7 mm. by 32 fi, 

 according to Thiele 2 mm. and over by 35-40 /(. In the type of Sollas reexamined 

 by me these amphioxes were 2.4-3.3, mostly 2.8-3.2 mm. long and 32-50 // thick. 



