84 NATURAL HISTORY SOCIETY OF DUBLIN. 



lobed ; but the lower end of Hobson's figure is less irregular, and not 

 quite like that of the upper. We have seen, indeed, that slight irregu- 

 larities sometimes occur in many of these forms, and I must confess I 

 hardly see grounds sufficient to retain Mr. Hobson's name. My im- 

 pression, then, is, that both the Hong-Kong plant and Docidium Pris- 

 tidce (Hobson) will eventually turn out to be nothing else than Triplo- 

 ceras gracile (Bailey). Those, indeed, who may not be disposed to 

 acknowledge Triploceras as a genus well distinguished from Docidium, 

 will call it rather Docidium gracile; but, to my knowledge, not any forms 

 yet described seem to show a transition or intermediate structure be- 

 tween the truncate extremities of Docidium (Breb.) and the lobed extre- 

 mities of Triploceras (Bailey) ; and until such a species presents itself, 

 so far as I can see as yet, the distinctions between thetwo genera seem 

 to be sufficiently well founded to be maintained. 



The following paper was also read : — 



Description op a New Species of Docidium (Breb.), from Hong- 

 Kong. By "William Archer. 



Family, Desmidiace^. 

 Genus, Docidium {Breb.) 

 Docidium Kayei (sp. nov.). 



Specific Characters. — Frond stout, about five times longer than 

 broad; segments with four whorls of prominent short stout hyaline 

 quadripartite spines, and a terminal whorl of hyaline simple spines ; 

 ends truncate. 



Locality. — Kowloon, on the mainland, opposite Hong-Kong. 



General Description. — Frond about five times longer than broad, 

 stout; suture forming a somewhat prominent rim ; segments about two 

 and a half times longer than broad, slightly and gradually tapering, 

 with four prominent transverse whorls of short stout hyaline quadri- 

 partite spines, their points divergent and subacute, and with a fifth 

 whorl, just under the ends, of short stout subacute simple spines; 

 ends broad, truncate. The margin of the body of the segments pre- 

 sents an undulate outline (including the terminal) forming five pro- 

 minences and four intervening depressions. It is of course only the 

 marginal prominences which impart this undulate outline — they really 

 form whorls (Mr. Kaye informs me ten in each whorl), and on their 

 summits are seated the hyaline quadripartite spines, forming gradual 

 continuations of the prominences, and which are here so characteristic. 

 The basal undulation, as is usual in this genus, is somewhat larger than 

 the others, which very slightly and gradually diminish upwards. The 

 terminal clear space in the endochrome large, circular, well-defined ; 

 active granules very numerous. 



Measurements. — " Length of frond ^ T , breadth ^^ of an inch " 

 (Kaye, in litt.). 



