295 



Rhynchozoon angulatum n. sp. 

 (PI. XXIII, figs. 4 a— 4 h). 



The zooecia, which consisl of a hard and thick calcareous mass and have as 

 a rule a rhombic hexagonal outline, have a strongly arched frontal wall, which 

 rises strongly i'rom the proximal end and from the lateral margins up towards 

 the oral rostrum or the oral avicularium. The margin of the zocrcium is provided 

 with a number of fairly large scattered pores and marks of two spines are some- 

 times seen distally to the aperture, which is approximately terminal. The aper- 

 ture, which is provided on each side with a more or less developed, as a rule 

 stout, conical projection, is almost circular in the greater part of its circum- 

 ference, but provided on its proximal margin with a slightly developed, low^ 

 rounded sinus. This on each side is bounded by a large, compressed cjuadrang- 

 ular hinge-tooth, the distal edge of which is provided as a rule with a small in- 

 cision dividing it into two lobes, only one of which can be seen from the frontal 

 aspect. From the distal rim of the aperture and a part of the lateral margins 

 arises a well-developed vestibular arch hanging down into the zoQ?cium, which 

 is provided on its oral surface near to the free margin with a row of small, 

 pearl-like nodules. The strongly chitinized, yellow operculum has two, small, 

 muscular pits on its distal half and is provided on each side of the slightly 

 marked sinus at the margin with an obliquely semicircular, thin region, arising 

 from the fact that this part has l)een in connection with the hinge-tooth. Each 

 distal wall is provided with 2 — 4 and each lateral wall in its distal half with 

 3 (2 — 4) uniporous or partly biporous rosette-plates, each of which is situated in 

 a small pore-chamber. 



The ooecia, the proximal part of which is very narrow, almost stalk-like and 

 gradually increases in width distally, have their basal part immersed in niche- 

 like hollows, the distal and marginal parts of their unperforated frontal surface 

 being furnished with an oa?cial cover arising from the distal zorecium and end- 

 ing in a curved or angularly bent proximal margin. The uncovered portion, the 

 greater part of which is of a yellowish colour, ends in an obliquely inwards di- 

 rected (fig. 4 f) trapeziform part with a straight proximal and incurved lateral 

 margins. 



Avicularia. A somewhat compressed avicularium, which is large, arched and 

 almost triangular in section, is found on one or other side of most zooecia in 

 the neighbourhood of the proximal rim of the aperture; its fairly long, triang- 

 ular mandil)le is directed oblicjuely outwards. In a smaller number of zoo-cia an 

 avicularium is either wanting or is placed on the proximal half of the zoa-cium. 



