Pherusa. Z. ASCIDIOIDA. 271 



Coast of Devonshire, Dr Coldstream. Stevenston, Ayrshire, 

 Rev. D. Landsborough. 



" Breadth nearly an inch, hispid ; the cells seem distributed over 

 the whole surface, and more vertical than the preceding ( Tub. pati- 

 na) ; there are, however, waved porous grooves, and the cells seem 

 disposed on each side of these in irregular transverse rows, united or 

 free, short, with expanding orifices dividing into irregular spinous pro- 

 cesses." Fleming. — I have two specimens of a polypidom, given to nie 

 by Dr Coldstream, which agree very well with this description, and are 

 figured in the plate referred to, but they adhere to a piece of sand- 

 stone, and were found in situ at low-water mark. The crust is half 

 an inch or a little more in diameter, and scarcely a line in thickness, 

 circumscribed by the thin very narrow edge of the basilar layer. It 

 is hard, calcareous, entirely adherent, of a greyish white colour, with 

 lighter slightly elevated roundish spots on the surface, or raised into 

 transverse ridges, conforming in this respect, perhaps, to the form of 

 the rock over which it spreads. The cells are barely visible with the 

 naked eye, erect, very close or coalescent, and not arranged distinct- 

 ly in any order. Their apertures are even with, or raised somewhat 

 above, the surface, circular, and armed on one side with three small 

 teeth, of which the central one is larger than the other. Many of 

 the cells are destitute of these, which are only perceptible when the 

 polypidom is viewed obliquely. 



The genus Discopora differs from Tubulipora in having cells in such 

 close and intimate union that they seem almost to be rather immersed 

 or excavated in the crust than separate tubes ; while from Lepralia 

 it estranges itself by the erect position of its cells, their tubular form 

 and non-constricted aperture, which, moreover, are at no season closed 

 with ovaries. The British species answers so well to Lamarck' s 

 definition of Discopora verrucosa, Anim. s. Vert. ii. 165 ; Stark, 

 Elem. ii. 436 ; that at one time I had concluded their identity to be 

 scarcely doubtful, but Blainville's figure (if correct) of the latter 

 proves the contrary, and represents a species with oblique ventricose 

 cells, similar in all apparent respects to those of a Lepralia, The fi- 

 gures I give of the natural size are very exact to nature, — that drawn 

 iinder the microscope is perhaps less characteristic, but there was no 

 possibility of communicating to it a greater verisimilitude. 



Pherusa tubulosa, Lamoiir. Corall. 53, pi. 2, fig. 1. Blainv. 

 Actinolog. 453, pi. 80, fig. 1. — Flustra tubulosa, Ellis 'AnA Soland, 



