DUBLIN NATTTEAL HISTOEY SOCIETY. 51 



sive years, and I have no doubt of its distinctness. I have several 

 times been asked the name of this species ; to afford a more satisfactory 

 answer than hitherto, the next time the question may be put to me, I 

 have no hesitation in assigning one to this pretty little species. 



On a former occasion (Nat. Hist. Rev., vol. v., p. 251) I had the 

 pleasure to name a species, for the ample reasons there given, after that 

 of my friend, George Porte, Esq. I was not then aware that Professor 

 De Bary, iu Germany, had anticipated me ; consequently, my name 

 for the species alluded to fell to the ground, and with it much of the 

 compliment I had intended. To restore the latter, I trust the present 

 attempt may be more successful. 



Genus — XANTHinruM {JEhr.). 

 Xanthidium Smithii ($p. nov.). 



Specific characters : Segments trapezoid ; spines minute, straight, 

 acute, marginal, in four pairs ; central projections minute, rounded, 

 tubercle-like. 



Locality : Numerous specimens were met with by me on a slide 

 marked "Wareham, 1849, W. S.," kindly lent to me by Professor 

 Harvey. 



General Description : Prond minute, in front view about as long 

 as, or very slightly longer, than broad ; constriction, a deep, gradually 

 widening notch ; segments about twice as broad as long, trapezoid, 

 lower margin somewhat convex, sides narrowing upwards and straight, 

 ends broad and straight ; spines short, minute, straight, acute, mar- 

 ginal, geminate, a pair placed on each of the four angles ; in side view, 

 segments about as broad as long, with rounded sides, ends truncate, 

 each upper angle furnished with a minute spine, beneath each of which, 

 about half way down the segment, there occurs another spine, all the 

 spines divergent ; end view sub- elliptic or broadly fusiform, ends trun- 

 cate, convex, furnished with three spines, the spines projecting, diver- 

 gent, none at the sides ; the central projection from each frOnt surface 

 a minute, rounded, smooth tubercle, apparent always in end view ; in 

 the side view the tubercles are sometimes concealed by the projecting 

 divergent central spines, while in the front view they are hidden by 

 the contained endochrome. Sporangium unknown. 



Measurements : Length of frond, y^JTe" ' ^^eadth, y^Vz °^ ^^ inch. 



Plate I. — Pig. 10, front view; Pig. 11, side view; Pig. 12, end 

 view. 



Affinities : This interesting little species seems to be allied on the 

 one hand to Xanthidium fasciculatum (Ehr.), and on the other to Arthro- 

 desmus octocornis (Ehr., Hass., Breb.) = Xanthidium octocorne (Ealfs), 

 var. /3, but is perfectly, and I believe, unmistakably distinct from 

 either. "With th^ former it agrees in the spines being subulate, mar- 



