19-21.] A. Robertson: Report on Bryozoa. 39 



15. Kinetoskias arabianensis, sp. nov. 



Zoariiim incomplete, consisting of a single stem with a few 

 branches at the distal end and breaking into a number of rootlets 

 at the attached end. The stem is composed of a number of radical 

 tubes, and of zocecia which are smaller and stifferthan the zocecia 

 of the distal branches, the two forming a stalk or stem which is 

 probably flexible in the natural state but sufficiently rigid to hold 

 the crown of branches two or more inches above the ocean-floor. 

 That the substratum in which this specimen grew is similar to that 

 usually described for Kinetoskias is shown by the globigerina and 

 other shells, and grains of sand adhering to the finest rootlets. The 

 branches at the distal end consist of zocecia in two series, the 

 zocecia of each series forming an acute angle with the zooecia of 

 the other. 



The adult or nutritive zooecia (Fig. 3, A) are very long and 

 may be considered to consist of two parts or regions, the zooecia 

 proper {zoe.) and the tubular base (t.ha.) more or less independent 

 of the former, and into which the polypide does not extend. 

 Indeed, the connection between it and the main body of the 

 zooecium is easih' and frequenth' broken, in which case the tubular 

 portion remains attached to the zocecium from which it sprang, 

 while the main portion is lost. Outlining each zooecium and thus 

 strengthening the rim is a chitinous border. At the point of 

 union of the zooecium proper and the basal prolongation, the 

 chitinous rim is frequently bent inward forming a weakened 

 place or break joint (b.j-)- At the distal end of the zooecium the 

 chitinous margin grows thinner and there forms a blunt point. 

 The wall of the zooecium is delicate and transparent, the orifice is 

 formed by the opening of a broadl}- semicircular lip bounded by a 

 heavy chitinous bar. Both sessile and pedunculated avicularia 

 occur. At the dorso-lateral angle of each zocecium there is a 

 sessile avicularium [ses.av.) with a mandible curved at the extre- 

 mity and fitting into a chitinous groove. This avicularium is seated 

 on a distinct area on the dorso-lateral wall to which the strong 

 mandibular muscle is attached and which is outlined by a delicate 

 rim (C, av.ar.). These avicularia frequently break off, in which 

 case the area is exposed. On a few zocecia only were frontal 

 pedunculated avicularia found, attached to the lower inner margin 

 (B, pcd.av.). These have an extremely short peduncle, but the 

 avicularia are relatively large. Through the transparent wall of 

 the zooecium the polypide is clearly visible especially in stained 

 preparations. Within the zocecium is found also a large and 

 powerful muscular organ (A,B, mus.). This is composed of two 

 groups of muscle fibres lying in the lower part of the zooecium 

 just above the tubular prolongation and spreading on two sides 

 of the median line like two fans. Viewed from the front, the 

 stomach of the contracted polypide is visible between the two 

 groups of muscle fibres (A, sL). 



In this colony there is but one fertile zooecium. It arises as 



