ZOOPHYTES. 31 



on the gonothecjB. It sometimes occurs on Stemrhyachux 

 rostratus between tide-marks. 



Plumularia Catharina, Jolmst. ; Hincks, Brit. H. Z. 

 vol. i. p. 299. 



Common on Asciclians, tubes of Thelejms, and the roots of 

 other corallines in deep water. 



Plumularia frutescens, Ellis & Solander ; Hincks, Brit. H. Z 

 vol. i. p. 307. 



Occasionally thrown on the West Sands after storms, and 

 also brought in by the deep-sea lines of the fishermen. The 

 smaller specimens are pale. One example is 6 inches in 

 height, and broadly branched. 



Order Medusid^. 



The Medusida; abound chiefly in autumn in the bay, the 

 most conspicuous amongst the larger forms being Aurelia and 

 Cyanea, the former often occurring in such numbers as to form 

 a closely packed layer on the surface of the sea over considerable 

 areas ; and though not in the dense party-coloured masses of 

 various species occasionally seen in the Hebrides, still they form 

 an interesting featm-e. At certain points the bay in quiet 

 weather is quite purplish with thousands, many of which are 

 loaded with ova; and through the transparent umbrellas the 

 abdominal feet of the parasitic Hyperidffi are observed in con- 

 stant vibration. Occasionally, whether from accident or de- 

 sign, one specimen is found adhering to the umbrella of another, 

 and is thus carried through the water. Moreover, on many of 

 the stones at the East and West Eocks, near low-water mark, 

 A^'Hydra tuba" is found, which maybe the hytboid condition 

 of the foregoing. This pretty little white structui-e, developed 

 from the ova of Aurelia and its allies, can be observed in all 

 stages not only throwing out lateral buds like a Hydra, but 

 by transverse fission dividing into a series of saucer-shaped 

 bodies which ultimately assume the form of the a.Mi Aurelia: 

 This form, it is well known, formed the subject of valuable 

 observations by the late Prof. M. Sars,and afterwards, amongst 



