17 



strengthened my previously expressed opinion that the oxyhexactine parenchyma- 

 lia of the Hyalonemas have been produced from true canalaria. It is remarkable 

 that these spicule^ , are confined to the walls of the incurrent canals and that 

 they are absent in the walls of the excurrents, where their place is taken by 

 certain forms of amphidiscs. 



Both surfaces of the lamella are uniformly covered with slender pentactine 

 pinules. The four basal rays, which form a rectangular cross, are on an average 

 50 /^ long and pretty stout. Their terminal parts are covered with short, oblique 

 spines directed outward. The free, radial ray varies in length. It bears rather 

 short, slightly divergent spines, which are longest in the middle of its spiny part. 

 From here they decrease in size towards its apex and also towards its smooth and 

 spineless basal part. Sometimes a sixth ray of varying length, directed inwards, 

 occurs, which generally resembles the basal rays. The dermal pinules of the 

 external surface differ from the gastral pinules of the internal surface chiefly in 

 the length of the radial distal ray, which measures in the former about 20O, in 

 the latter 400-600 /^ and more in length (pi. XIX, f. 9, 10). 



As the sharpened, free margin of the sponge has been lost, I cannot say 

 anything about the mai'ginalia which probably composed it in the living sponge. 



Macramphidiscs are absent in the dermal membrane but occur scattered 

 throughout the parenchyme. They are on an average 350 /* (300-400 ^ ) long. 

 The shaft usually bears in the middle, where it is thinnest, a ring of sharp 

 spines ; apart from these it is smooth. The rather flat terminal discs are about 

 60 M high, on an average 120 i^ broad and have eight broad, spade-like marginal 

 teeth (pi. XIX, f. 8). 



Ellipsoidal mesamphidiscs of varying size, on an average 40-60 /* long, are 

 very abundant and regularly arranged. The shaft is slender and covered with 

 numerous small, sharp spines. In the centre there is a ring of longer, mostly 

 curved spines. The high, bell-shaped terminal discs have 8-10, usually narrow 

 marginal teeth 10 ^ long (pi. XIX, f. 5-7). As in Hyalonema rapa and 

 fi". martabanense these amphidiscs are arranged in a single layer which coats 

 the larger excurrent canals. It is true that they appear somewhat irregularly 

 scattered in my sections, but still I believe that in the living sponge most of them 

 were placed vertically in the canal-wall, in such a manner that one-half of each 

 mesamphidisc was imbedded in the sponge-tissue whilst the other half projected 

 freely into the cavity of the canal. The narrower incurrent canals are destitute 

 of such a coating of mesamphidiscs (pi. XIX, f. 2). 



The micramphidiscs are scarce and lie scattered irregularly in the dermal and 

 gastral membrane ; a few are also found in the choanosome. They are about 

 20 M long and have hemispherical terminal discs with numerous marginal teeth 

 (pi. XIX, f. 2, 4). 



