44 



margins of the two opposite spade-like anclior-teeth, whicli are continued 

 proximally so as to join each other in the middle, at the sides of the shaft. 

 In Se^nperella schultzei these margins are either quite smooth, or have only 

 one or two slight indentations distally, and are strongly indented centrally, 

 where they join. In SemjpereUa cucumis they are serrated distally by numerous 

 projecting lateral t.eetli and protrude, where they join centrally, outwards and 

 upwards (pi. VIII, f. 9). 



In the dermal membrane and the oscular sieve-plate stout pinules are every- 

 where numerous. Their length differs considerably in different parts of the 

 dermal surface. It is here usually 200-;j00 ^ . Their basal rays, which form a 

 rectangular cross, are stout, straight, distally covered with tubercles or short 

 spines, and also of varying length. They usually measure 60-80 /^. On the 

 oscular sieve-plate pinules of considerably greater length, measuring 400-450 /^, 

 are met with. The main ray is covered with stout, obliquely-diverging spines, 

 and resembles an Italian poplar (pi. VIII, f. 12-13). The basal part of this ray is, 

 for a length of usually less than 40 p-, free from spines, smooth, and on an average 

 6-10 Z'' thick. The terminal spine is not joarticularly long, and not much thick- 

 ened. A curvature of the basal rays, giving to them the appearance of an 8, 

 as in the pinules on the slender dermal strands of Semjperella schultzei* has never 

 been met with in the pinules of Semperella cucumis. 



The dermal and oscular macramphidiscs are large, stout and — particularly on 

 the free ends of the tube-walls — numerous. Their terminal discs are approxi- 

 mately hemispherical, distally somewhat flattened, and have 8 broad spade-like, 

 terminally-rounded marginal teeth. The shaft is pretty stout, knotty, but with- 

 out any conspicuous protuberances in the centre (pi. VIII, f. 4). 



True mesamphidiscs are entirely absent ; micramphidiscs, however, are 

 frequent. These differ considerably in size, but are all pretty much of the same 

 shape. They are 20-40 /* and more long, and their terminal discs are hemi- 

 spherical, have 10-12 marginal teeth, and are G-12 /-^ broad. The shaft is 

 slender and usually slightly tuberculous (pi. VIII, f. 5, 6). 



It is a characteristic peculiarity that numerous spined oxypentactines, oxyte- 

 tractines (stauractines) and spindle-shaped diactiues are contained in the layer — 

 of which the walls of the ciliated chambei'S form a part — dividing the incurrent 

 from the excurrent system. The two limiting-membranes of this layer are nearly 

 parallel to each other. Both are similarly chiefly supported by oxypentactines. 

 Their basal (paratangential) rays are covered with small, vertical spines. 

 They are at the base 8-12 /* thick and gradually attenuated towards the sharp- 

 pointed end (pi. VIII, f. 8). Their length varies from 100-200 /^ , the basal rays 

 of one and the same spicule, however, are usually of equal length. The apical 

 main ray is vertical to the basal rays and points inward ; it is spined, and in 



* Challenger Reports, Hexactinellida pi. LIT, f. 6. 



