440 PROP. J. A. THOMSON AND MR. W. D. HENDERSON ON [Apr. 10, 



The stalk is uncoloured and covered by irregular longitvidinal 

 ridges. There is evidence of a slight basal expansion, but this 

 may be partly due to a contraction of the basal ccenenchyma, 

 through which the end of the axis has been thrust. There is a 

 slight swelling at the top of the stalk. The central axis (almost 

 1 mm. in diameter) tapers markedly for the last 4 millims., and 

 ends in a twisted coil. 



The metarachidial surface shows (1) an almost bare sti'eak 

 about 1'75 mm. in breadth, with a few (seven) zooids in a single 

 row towards the upper end ; (2) a deep median furrow which is 

 evaginated as a ridge towards the base, doubtless a post-mortem 

 result; (3) fine, close-set, longitudinal striations, about 12 on 

 each side of the middle line ; (4) scattered superficial spicules. 

 The median zooids have a diameter of about 0*25 mm., and show 

 no trace of tentacles. 



The prorachidial surface has a bare space about 2 millims. in 

 diameter ; it shows a deep median groove, longitudinal striations 

 less marked than on the other side, and a few irregvilarly- 

 scattered spicules. The end of the prorachidial insertion of the 

 pinnule is almost on a level with the metarachidial insertion. 



The zooids occur on the inferior surface of the pinnules, and 

 their insertion is what is termed median. Beginning with a 

 cluster at the prorachidial insertion of the pinnule, they rise in a 

 narrow crescent away from the base and descend gradually to the 

 metarachidial insertion. They are white in colour and stand out 

 like little octoradiate stars. 



This species falls into KoUiker's second section with median 

 zooid-plates and into the group Pt. pellucidu.m. It comes nearest 

 Pt. gracile, but diflers from it in many features, e. g. in having 

 four main rays instead of 7-9, in having one I'ow of marginal 

 polyps instead of two, in having a very short zooid streak instead 

 of a very long one (25 millims.). 



Locality. Wasin Channel, 10 fathoms. 



Literature referred to. 



1900. AsHwoRTH, J. H. — "The Xeniida?." Willey's Zoological 



Results, pai't iv. 

 1834. Ehrenberg, C. G. — Die Corallenthiere des Rothen Meeres. 

 1870. Gray, J. E. — Catalogue of the Lithophytes or Stony Corals 



in the British Museum. 

 1887. Grieg, J. A. — " Bidrag til de Norske Alcyonarier," in Ber- 



gens Museum Aarsberetning. 

 Herklots, J. A. — Notices : Polypiers nageurs ou Penna- 



tulides. 

 1894. IIiCKSON, S. J. — " A Review of the Genera of the Alcyo- 



naria Stolonifera." Trans. Zool. Soc. London, vol. xiii. 

 1900. Ibid.—'' The Alcyonaria and Hydrocoi-allinas of the Cape 



of Good Hope." Marine Investigations in South Africa, 



vol. i. 



