Dr. J. R. KiNAHAN on the Genus Oldhamia. 



.557 



This form differs from Old. antiqua in its more crowded fans of branchlets, 

 whicli nearly completely conceal the stem, the branchlets are flexuous, but 

 at the same time more delicately filiform ; tlie whole polypidom, in short, more 

 delicate. 



The distinctions between the two are similar to, but much more markeil 

 than, those between well-marked specimens of Serlularia argentea and Sertula- 

 ria cupressina. However, in instituting this comparison it should be borne 

 in mind that Oldhamia antiqua approaches in appearance Serf, argentea more 

 closely than Sert. cupressina, Old. discreta being even finer than Sert. argentea, 

 and not resembling Sert. cujjressi7ia. 



No forms intermediate between Old. ayitiqua and Old. discreta have oc- 

 curred to me, which confirms the idea of their being distinct. Badly marked 

 specimens of Old. discreta cannot without difficulty be distinguished from some 

 forms of Old. radiata. The best marked specimens I have seen are those in 

 the geological collection already referred to ; but I believe I have met the 

 species myself at Graystones, in the railway cutting, where the form to which 

 I would restrict the name of Old. antiqua also occurs, but rare. 



Oldhamia radiata {Forbes). Figs. 3, 4, 5, 8, 9, 10. 



Polypidom gregarious (?) ; many branched ; branchlets arising from com- 

 mon point ; cells biserial, alter- 

 nate, branchlets (o) dichoto- 

 mous, arranged in form of a star; 

 (^) (Fig. 4) branchlets irregu- 

 lar, patent, markedly dichoto- 

 mous, thickened at the ends, the 

 whole polypidom creeping. 

 Oviferous capsules (?) axillary, 

 elliptical. Locality : Bray, Gray- 

 stones, Co. Wicklow. 



There are many well-marked forms of this, but intermediate forms con- 

 nect them with each other. Figs. 3, 5, 8, 10 exhibit the ordinary and most 

 typical form. 



Fig. 8. Oldhamia radiata.~Ox^\n-iry inTm. Br.ay Head. 



VOL. XXIII. 



4d 



