334 DISCOVERY REPORTS 



Genus Psammatodendron, Norman, 1881 



77. Psammatodendron indivisum, sp.n. (Plate VII, fig. 16). 

 Three stations: WS 92, 213 (fragments ?), 243. 



Test consists of a long, unbranching, very narrow thin-walled tube emerging from a 

 rather large depressed circular primordial chamber. The tube increases slightly in 

 diameter in the course of its growth and is composed of extremely minute sand grains 

 mixed with cement, pale brown in colour, flexible in life, rather brittle in dried speci- 

 mens. Aperture simple at the termination of the tube, which is here apparently some- 

 what constricted. Average length of tube 1-50 mm. Average diameter of primordial 

 base 0-25 mm. 



A few examples only of this little organism have been found attached to stones, etc. 

 It is probably not uncommon, if specially searched for, but is not easily detected among 

 other sessile organisms. 



P. indivisum differs from the genotype P. arborescens (B. 188 1, HNPE, p. 98) in its 

 unbranching habit and large depressed primordial chamber. It might perhaps be 

 assumed that the unbranching specimens found were merely young individuals of 

 P. arborescens, but in that case it would be expected that plentiful fragments of the 

 branching colonies would be found in the dredged material. This is not the case, nothing 

 suggesting a branched fragment of P. arborescens has been seen. The depressed shape of 

 the primordial chamber of P. indivisum is also very characteristic. Brady figures that of 

 P. arborescens as a bulb, and describes it as a "more or less inflated chamber". From 

 the many examples in our gatherings at Millport, we can say that the primordial chamber 

 of P. arborescens is extremely difficult to find at all. The organism usually starts abruptly 

 with a tubular outgrowth from its surface of attachment. 



Genus Marsipella, Norman, 1878 



78. Marsipella cylindrica, Brady. 



Marsipella cylindrica, Brady, 1882, FKE, p. 714; 1884, FC, p. 265, pi. xxiv, figs. 20-22. 

 Marsipella cylindrica, Heron-Allen and Earland, 1912, etc., NSG, 1912, p. 3S8, pi. v, figs. 8, 9; 

 pi. vi, figs. 8, 9. 



Three stations: 228; WS 99, 215. 



Fragments only. At WS 99 they are larger than usual and built up of sand grains and 

 sponge spicules, whole and broken, irregularly arranged. At 228 the specimens are 

 smaller and almost entirely constructed of spicules neatly cemented together. 



Genus Rhabdammina, M. Sars, 1869 



79. Rhabdammina abyssorum, M. Sars. 



Rhabdammina abyssorum, M. Sars, 1868, LUHD, p. 248; G. O. Sars, 1871, HP, p. 251. 

 Rhabdammina abyssorum, Brady, 1884, FC, p. 266, pi. xxi, figs. 1-13. 



One station: WS 225. 



A single three-rayed specimen, more neatly constructed than is usually the case with 



the North Sea type, the sand grains being small and almost uniform in size. 



