180 



always without acropetal spines. A well — developed oral shell'. The aperture, 

 measuring ahout one-fourth of the entire length of the zocecium has a hroad and 

 deep, rounded sinus, the cui\e(l line of wliicli would sometimes meet the rest of 

 the margin in a circle, if it was not separated from the latter hy the well-deve- 

 loped hinge-teeth. The proximal part of the operculum is on either side furn- 

 ished with a short chitinous sclerite. The cryplocyst, which has rather small, 

 widely scattered pores and small dispersed tubercles, has a distinctly projecting 

 marginal i)orlion, without distinct crenulation. Of the two o[)esiul£e the larger 

 is at least twice the breadth of the other and formed like a long rounded trape- 

 zium. The opesiuiar outgrowths both reach the basal wall, which they gene- 

 rally meet in a continuous transverse line, occupying the entire bieadth of the 

 wall (tig. 7 i). The unusually narrow poIy|)ide-tuI)e has an almost smooth and 

 [)roximally much depressed frontal wall, and contrary to the common rule in 

 this genus it has a basal wall of its own, which is liowever in the majority 

 of the zoa^cia very short, sometimes almost imperceptible, and at most attains 

 half the length of the entire polypide-tube. Otherwise tiie poly[)ide-tube is only 

 re[)resented by its frontal wall. 



The spicules (fig. 7 c), which only seem to be present in the zocrcial cavity, 

 occur both in the shape of curves and of comi)asses. The length of the latter 

 may vary between 0,099 and 0,305'""' and the curves, which are unusually 

 thin with sharply bent ends, measure from 0,039 to 0,179™™- The dimensions 

 of both forms are a little different in the variety with |)rismatic branches. 



The ooecia have, when seen from the front, a broad, obcordate outline, and 

 a horizontal, rounded triangular, aperture whose somewhat protruding lateral 

 margins meet into a roof-sha|)ed ridge continued some way along the uuddle of 

 the ooecium, thus giving the whole of this portion a sagittal outline. The short 

 gonozooecia have two opesiulse of about the same size and a semi-oviform ope- 

 ning with a comparatively narrow sinus. Their membranous operculum has a 

 little within the margin a narrow continuous chitinous arch. The gonozooecia 

 occur in continuous rows, separated by twos by a row of ordinary zooecia. 



The avicularia, which may attain a length similar to that of the zoa>cia, 

 while their breadth is considerably smaller, have a vase-shaped mandible, the 

 opercular arch of which has the form of an isosceles triangle with the legs 

 meeting a little inside the point. The shape of the posl-opercular opening of 

 the cryptocyst may vary a good deal, being sometimes rounded ([uadrangular 

 and sometimes forming part of an oval. On the other hand the proxinud margin 

 of the well-develoi)ed distal cryptocyst always forms part of an oval. 



The colonies may occur both incrusting and free, in the latter stale some- 



