SIPHONACE^. 23 



latter genus, after the lime has been removed by acid, there remains a plexus of 

 unicellular, branching filaments, filled wtth green endochrome, and essentially of the 

 same structure and nature as those of Codium. In C. Opuntia these filaments are 

 easily extracted, and may readily be pulled asunder ; in C. Tuna they adhere more 

 closely and require to be carefully manipulated. The Halimedce, like the Caulerpce, 

 are confined to the warmer portions of the globe, and are particularly abundant on 

 coral reefs, in both hemispheres. As many as thirteen species are described by authors, 

 but several appear to have been founded on very insufiicient data ; and probably they 

 might be reduced by one-half. C. Opuntia is the most widely dispersed, being found 

 abundantly in the tropical Atlantic and Pacific, and in the Mediterranean and Red 

 Seas. C. incrassata and C. Tuna occur in the Pacific as well as in the Atlantic, but 

 are less universally dispersed than C. Opuntia. When seen in herbaria the species are 

 frequently bleached white, but all are of a bright grass-green when growing. They 

 are furnished with deeply descending, fibrous, much branched roots, whose capillary 

 rootlets firmly grasp particles of sand, and with them form a solid ball, not easily 

 broken asunder. 



1. Halisieda Opuntia, Lamour. ; frond very much branched, diffuse ; articulations 

 reniform, flat, obscurely lobed or repando-crenate along the upper margin. Lamour. 

 Exp.Meth.,p.21,t.20,fig.Q. JDne. Cor. p. 90. Kiltz. Phyc. Gen. t. 48, Jig. 2. 

 Kiitz. Sp. Alg. p. 504. Corallina Opuntia, Ellis and Sol. p. 110, t. 20, Jig. b. Ellis, 

 Cor. t. 25, a. (Tab. XL. B.) 



Hab. On rocks and in tide-pools, near high water mark, on the Florida Keys. 

 Key West, W. H. H., ProJ. Tuomey. (v. v.) 



Root deeply descending, fibrous, densely compacted into a fusiform mass, 1-2 inches 

 long. Stems very numerous from the crown of the root, weak, but supporting each 

 other by their proximity, and thus forming very dense tufts, much and irregularly 

 branched ; the branches spreading. Articulations, qxcq^Io^iq or two of the basal ones, 

 which are oblong or cylindrical, broadly reni-form, the more normal ones twice as 

 broad as their length, from | to more than \ inch across, flat, rather thin, but much 

 incrusted with calcareous matter, with a more or less evident or obsolete longitudinal 

 ridge through the middle ; the superior margin somewhat repando-crenate or lobed. 

 After the calcareous matter of the frond has been removed by acid, a spongy vegetable 

 structure remains, made up of a plexus of slender, longitudinal, unicellular filaments, 

 constricted at intervals, and at the constrictions emitting a pair of opposite, decom- 

 pound, dichotomous, corymboso-fastigiate, horizontal ramelli, whose apices cohere 

 together, and form a thin epidermal or peripheric stratum of cells, over the surface of 

 the frond. When the surface is viewed vertically, the cohering tips of the ramelli 

 appear like the areoli of a continuous membrane. The substance of the filaments is 

 tough, and they are filled with green matter. No fructification has been observed. 



