384 PERCY SLADEN TRUST EXPEDITION. 
distribution on the west coast of Europe. The true Codiwm tomentosum has small utricles 
up to 500 » in length and ranges as far north as Great Britain, whereas C. elongatum 
has large utricles, often twice as long as those of C. tomentosum, and does not seem to 
occur north of Cadiz. We find the same distinction to hold good for extra-European 
species. 
TYDEMANIA, Weber van Bosse. 
22. Tydemania expeditionis, Weber van Bosse, in Aun. Jard. Bot. Buitenzorg, xvii. 
(ser. 2, vol. ii.) 1901, p. 189. (Plate 48. figs. 18, 19.) 
Amirante, 20-44 fms. Chagos Archipelago: Salomon, on reefs exposed at dead low 
tide. 
Geogr. Distr. Malay Archipelago. 
For the sake of convenience we quote here the original diagnosis of this rare alga :— 
“ Thalle incrusté de calcaire, composé d’un axe cylindrique simple ou ramifié, portant 
des branches réunies en glomérules superposés ou rarement disposés en éventail. 
Branches se divisant par dichotomie répétée en directions alternantes en ramules tres 
étalés, enchevétrés, formant un glomérule dense, ou branches se divisant par dichotomie 
répétée en une seule direction en ramules érigés, conglutinés, en forme d’éventail. 
Fructification inconnue.” 
This plant seems to have eluded the observation of collectors until discovered and 
recorded by Madame Weber van Bosse when on the ‘Siboga’ Expedition to the Dutch 
East Indies, and it was briefly described by her in the diagnosis quoted above. The 
specimens which she has been so kind as to lend us show the remarkable dimorphic 
habit of the plant, and they will be figured among the ‘Siboga’ reports. But while 
her specimens chiefly represent the glomerulous form, those of Mr. Stanley Gardiner 
are of the flabellate form only, without a single example of the glomerulous form, and 
consist of tufts and masses of small flabellate calcified fronds connected together by 
a continuous branched filament. At first sight these flabella might easily be mistaken 
for Udotea javensis, Gepp (Journ. of Botany, xlii. 1904, pp. 363-4, pl. 467), formerly 
known as Lhipidosiphon javensis, Mont., since they consist, like that species, of calcified 
dichotomously branched filaments, adhering laterally in one plane. The stipes also, 
upon which the flabellum in each species is borne, is monosiphonous. But a comparison 
of the two species side by side shows at once unmistakable differences. In 7. expedi- 
tionis the single siphon, which bears the flabellate fronds, is beaded from its point of 
junction with the main filament up to the point at which it divides to form the 
flabellum, while in U. javensis the monosiphonous stipes is entirely unbeaded and often 
emits rhizoids, as may be seen in our figures of the plant (loc. cit. figs. 2,3). In the 
size of the filaments, both ‘of stem and frond, there is considerable difference between 
the two species. The diameter of the stipes in 7’. expeditionis is about 250-280 » and 
of the frond filaments 40-70 », while that of the stipes of U. javensis is 60-100 » and of 
the frond filaments 30-40 p. 
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