86 COLLINS AND HERVEY. 



thin and membranaceous to coarse and leathery; the dark, zonate 

 lines are distinct in the thin, light colored form, imperceptible on the 

 old, coarse and dark fronds. It differs much in the extent of division 

 of the fronds, from broad-cuneate and little parted, to fronds consisting 

 of innumerable narrow divisions, sometimes broad below, narrow 

 above, always more or less cuneate with apex truncate. Under water 

 it shows a very brilliant iridescence of peacock blue and green. 



PADINA Adanson. 



1. Epidermis persistent as an indusium over the spores. 2. 



1. No indusium; spore band in middle of each second zone between bands 



of hairs. 4. P. gymnospora. 



2. Frond dark and thickish, not much calcined; in middle part 2-3 cells 



thick; bands of spores alternating with bands of hairs. 3. P. variegata. 



2. Lighter colored and thinner; distinctly calcined. 3. 



3. Band of spores above each second band of hairs; frond normally 2 cells 



thick. 1. P. sanctae-crucis. 



3. One band of spores above and one below each second band of hairs; frond 



normally 3 cells thick. 2. P. Pavonia. 



1. P. SANCTAE-CRUCIS Borgesen, 1914, p. 201, figs. 153-154; 

 P. B.-A., No. 2082. Harris Bay, Jan., Nov., Hervey; Shelly Bay, 

 April, Jew's Bay, Ely's Harbor, Hungry Bay, July, Gravelly Bay, 

 Aug., Collins. A rather thin, delicate species, growing mostly in 

 shallow, quiet water. The color is usually a quite light yellowish 

 brown on the upper side, the under side being usually covered with a 

 continuous but quite thin calcareous coating, white or bluish in color. 

 The dried plant is papyraceous and brittle. Only tetrasporic fruit 

 has been found, which was on plants collected in July and August. 

 The indusium consists of the epidermis, which is pushed up by the 

 spores as they grow, and finally ruptured; being very thin and trans- 

 parent it is not always easy to make out, but it often happens that 

 when it is pushed away from the frond, it retains the markings out- 

 lining the layer of cells beneath; in such case a fine network corre- 

 sponding to the cells can be seen with the microscope by careful 

 focusing, on a level with the top of the spores. This form of indusium 

 has been noted in Zonaria variegata by Sauvageau, 1905, p. 11 (of 

 reprint.) 



2. P. PAVONIA (L.) Gaillon, 1828, p. 371; Harvey, 1846-51, PI. 

 XCI; P. B.-A., No. 2081; Fucus pavonius Linnaeus, 1763, p. 1630. 



