5.58 Dr. J. E. Kinahan on the Genus Oldhamia. 



Sometimes in place of the branchlets proceding from the same point, the 

 whole polypidom is lengthened upwards, but without a central axis, resembling 

 Sertularia operculata among recent species. When the branchlets are much 

 divided, this form might be mistaken for Old. antiqua ; a badly marked specimen 

 of it is seen near the letter X on the slab figured as No. 5. 



Sometimes a single branch is elongated, as is seen in Fig. 10 ; this form 

 proves the necessity for uniting the well-marked variety just described, and the 

 typical form. In the variety figured at {a) (Fig. 5), the cells are simply 

 placed end to end, witliout any branchlets, and the whole polypidom is long 

 and unbranched ; this stem sometimes, as it were, breaks out into branchlets, 

 which are then arranged in a stellariform manner. I think it probable that this 

 form was creeping. An interesting modification of this is, that in which the 

 unbranched axis springs from the centre of one of the ordinary typical speci- 

 mens, and then itself bears a star on its summit ; workers among recent species 

 are well acquainted with similar, as they are called, proliferous polypidoms, 

 especially among the Sertularian Hydrozoa. 



There is yet another remarkable form, indicated as form (^) in the descrip- 

 tion of the species, viz., that in which (Fig. 4) the polypidom is procum- 

 bent and repent ; the dichotomous branchlets developed numerously along one 

 side, but with great irregularity, these branchlets being markedly dichotomous, 

 also much thickened at the ends. The intermediate forms forbid tliis being 

 separated from the type except as a variety, — especially as similar differences, 

 as before remarked, exist between forms of recent species. 



Distortion, probably arising from cleavage, in this as in other fossils, exerts 

 occasionally a remarkable influence over form. One specimen is figured 

 ( Fig. 9) from a much contorted red schistose bed at Bray. 



In certain specimens, as, for instance, that figured as Fig. 10, in the axils of 

 the cells, of which the branchlets are composed, occur certain elliptical bodies, 

 best seen in the casts of the fossils : these I am inclined to believe are oviferous 

 capsides ; tliey are rare, and still more rarely well marked ; probably, when 

 attention is called to them, they may be better made out. I have not met them 

 as well marked in Oldhamia antiqua., but traces of them occur. 



The remarkable diflerences in physical characters between the beds in which 

 Oldhamia radiata occurs, and those in which alone Oldhamia antiqua is met 



