226 



description refers, hiil Ihcy are foiiiul in some eolonies of Ihe variety setigera 

 originating from the same |)laee, wliieli among other things dillVr IVom Ihe main 

 form in having the lateral chamhers extended over more than two-lhirds of the 

 basal side of the zocecium and their membranous walls ending in a number of 

 scattered chitinous denticles. 



A gonozofficium with its covering kenozooecium bears a certain resemblance 

 to a helmeted head and springs from a single zon-cium, which again springs 

 from the mother-zooecium of a bizotecial segment. The gonozocecium and the 

 covering kenozocecinm are of al)()ul the same size, and a transverse section 

 through the centre of the entire complex has the form of a I'onndcd trapezium 

 with a larger frontal and a smaller basal side and with two sides converging 

 basally. The wide aperture, the operculum of which has a more strongly chitin- 

 ized marginal portion, is shared in common by the gonozooecium and the keno- 

 zooecium. It is bounded by a nujre strongly arched distal and a less strongly 

 arched proximal margin, in the centre of which there is a short sulural line 

 passing on to a small, transversely oval pore. The sternal area has 6 — 7 pear- 

 shajjcd fenestra; disposed in an angle, of which the two distal are situated on a 

 level with Ihe median pore. The lirsl j)air of ribs, which limit the aperture 

 proximally, pass without any distinct boundary into the broadly rounded inner 

 cryptocyst lamina, while Ihe second pair of libs, which are provided with an 

 acutely projecting terminal part, meet in the above-mentioned suture on the 

 proximal side of the aperture. Finally, the gonozooecium is on each .side provided 

 with two large, flat, generally lra|)eziform lateral chambers (fig. 1 1), of which 

 the dislal, which has 10 — I'l rosetle-|)lales, coiresponds to Ihe three distal lateral 

 chambers and the proximal, with about 10 rosette-plales, to the pedal chamber. 

 The real oo'cium is the helmet-shaped, arched distal wall of the gonozo(L'cium, 

 the jjroximal, oblicpiely ascending part of which is provided wilh a very large 

 number of uni|)orous rosette-plates. This oa'cium is again covered l)y a keno- 

 zoo'cium, in which we may distinguish between a large, uncalcificd, saddle-shaped 

 or liorse-shoe-shaped central i)ortion and two ])roximally continuous, but distally 

 widely separated, calcified portions, a frontal and a basal one. The IVonlal sur- 

 rounds the aperture dislally and is composed of two strongly arched lateral halves, 

 which from their proximal part, situated dislally lo the Iwo lateral chambers, 

 decrease in breadth towards the frontal end and are connected only by a very 

 low portion on the distal side of the aperture. The basal part, which is bent 

 towards the frontal side and which seen from the side is like the crest of a 

 helmet, is rather narrow, frontally pointed and bounded by two curved, lateral 

 margins (fig. 1 in). On either side between the two calcified jjortions the o(iH-iuni 



