HO HILDENBRANDTIA. 



most developed of this parasitic section of the genus, and perhaps, without 

 much violence, the three preceding species might be considered as merely 

 younger and imperfect forms. Dr. Johnston goes much further, and re- 

 fers the whole to Corallina ojficinalis. This plant, says he, " appears first 

 in the guise of a thin, circular, calcareous patch of a purplish colour, and 

 in this state is common on almost every object that grows between tide- 

 marks. When developing on the leaves of Zostera, or in other unfavour- 

 able sites, these patches are usually pulverulent and ill-coloured, green or 

 white, and never become large ; but in suitable situations, they continue 

 enlarging in concentric circles, each marked with a pale zone, until they 

 ultimately cover a space of several inches in diameter. The resemblance 

 which, in this condition, the crust has to some crustaceous fungi, more es- 

 pecially to Polyporus versicolor, is remarkably exact, and neither is it less 

 variable than the fungus in its growth, the variations depending on the na- 

 ture of the site from which it grows. If this is smooth and even, the folia- 

 ceous coralline is entirely adnate and also even, but if the surface of the 

 site is uneven or knobbed, the coralline assumes the same character. If it 

 grows from the edge of a rock, or on the frond of a narrow sea-weed, or from 

 the branch of the perfect coralline, the basal lamina spread beyond in over- 

 lapping imbrications of considerable neatness and beauty : they are semi- 

 circular, wavy, either smooth or studded with scattered granules, and these 

 granules [ceramidia] may be either solid or perforated on the top. Such 

 states of the coralline have been described as Millepora lichenoides ; while 

 its earlier states constitute Lamouroux's various species of Melobesia." 

 Johnst. Brit. Lith. p. 220. 



IV. HILDENBRANDTIA. Zanard. [Plate 14, C.j 



Frond cartilagineo-raembranaceous (not stony], crusta- 

 ceous, suborbicular, adhering by its lower surface ; composed 

 of very slender, closely packed, vertical filaments. Concep- 

 tacles immersed in the frond, orbicular, depressed, pierced 

 by a hole, and containing tetraspores and paraphyses at the 

 base of the cavity. 



1. H. rubra, Meneg. ; Mem. Riun. Nat. Padov. 1841, p. 

 10; Harv. Phyc. Brit. t. ccl. Rhododermis Drummondii, 

 Harv. in Ann. Nat. Hist. vol. xiv. p. 27, t. 2. 



On smooth stones and pebbles between tide-marks, and in deep water. 

 Common. Forms a thin, membranous crust, at first orbicular, and spread- 

 ing concentrically, at last irregular in form, following the sinuosities of 

 any body to which it may be attached. A small portion, viewed vertically 

 under the microscope, shows minute cells, lying in clear jelly. When in 

 fruit the surface is pitted with disk-like depressions, pierced by a hole 

 which communicates with a chamber in which the spores lie. Colour va- 

 riable ; now a bright, now a dull red. 



Sub-order 3 ? LITHOCYSTE.E. Frond plane, hyaline, com- 

 posed, of cells radiating from a centre. Fructification un- 

 known. 



