120 DICTYOTACE^.— Hydroclatheus. iv. 



and having thin walls. The outer stratum in which the colour resides is very thin, 

 composed of exceedingly minute cells, with square ends, but whose exact shape I 

 could not well determine. Dr. Montague, in his splendid work on Algerian Algae, 

 says that they are parallelipipeds, placed, with their smaller ends to the circumfer- 

 ence. With the views respecting this species entertained by Dr. Montague and 

 expressed in that work I fully concur, and now proceed to describe this curious 

 vesretable in detail. 



1. Hydroclathrus cancellatus, Bory. — Mont. Alg. Algier. p. 36. Asperococcus 

 dathratus,J. Ag. Sp. Alg., vol. l,p. 75. Enccelium clathratum, Ag. — Kictz. Sp. Alg. 

 p. 552. Halodictyon cancellatum, Kutz. Phyc. Gen. p. 338. (Tab. IX. A.) 



Hab. Subtropical. On rocks, etc., in tide pools near low-water mark. Annual. 

 Sand Key, Florida, abundant in February. W. H. H. (v. v.) 



Fronds of irregular form, oblong or sinuous, two to three inches in length and 

 about an inch high, heaped together in wide-spreading patches, adhering to the 

 rocks by the lower surface, and to each other by their sides. The young fronds, 

 in the earliest stage at which they were found, are pierced by rounded holes, of 

 small size and somewhat pressed together. As the membrane expands, the original 

 holes expand also, and grow wider, and new holes are formed in the interspaces, 

 until the whole membranous wall of the bag-like body is converted into a 

 delicate, lace-like network. The margin round each hole is strongly involute, which 

 gives the appearance of a thickened rim, when the membrane is viewed vertically. 

 The substance is thick, crisp to the touch at first, but very fragile, and it soon 

 changes colour and loses rigidity on exposure to the air. The surface-cells are 

 exceedingly minute, filled with colouring matter ; those that compose the thickness 

 of the membrane are of large size, hexagonal, with thin walls and full of watery 

 juice. No fructification was observed on my specimens. The colour when 

 growing was a very pale, yellowish- olive, somewhat ochraceous. This rapidly 

 changes, and the plant becomes dark brown in a dried state. 



Our figure gives a tolerable idea of the Sand Key plant, as to size of individual 

 fronds and mode of composition of the patches : but I have failed in making it suffi- 

 ciently lace-like, and in giving the effect of depth to the holes Avhich pierce it in every 

 direction. I have some doubts whether all the plants known under the name H. 

 cancellatus are identical. The beautiful figure in the great French work on Egypt, 

 would not at all answer any specimen of the Sand Key plant which fell under 

 my notice. But it must be borne in mind that my specimens were gathered early 

 in the season, and were comparatively young ; and, therefore, it is possible that 

 later in the year they might have put on a very different aspect. If all the 

 clathrate Algse referred to this place by botanists belong to the present species, it 

 has a wide range ; being found through the warmer parts of the Atlantic at both 

 sides ; in the Mediterranean ; the Red Sea ; on the shores of the Mauritius, and 



