Dr. J. R. KiNAHAN on the Genus Oldkamia. 551 



After a careful examination of a great number of the recent Pulyzoa, I 

 have never yet met a species which approaches these fossil forms, Dor can I 

 perceive in Oldhamia the minute structure spoken of by Forbes as more in ac- 

 cordance with the Polyzoan alliance than the Hydrozoan. There is among 

 the collection of the Geological Survey of Ireland a fossil marked from the beds 

 at Carrickmount, but which is yet undescribed, and more like a Polyzoan than 

 a Sertularian ; perhaps this may have been the specimen which was under 

 FoKBEs's eye when he penned those remarks. I have not described this till I 

 have seen more specimens, and know more about its locality, but it is certainly 

 unlike Oldhamia. 



The mode in which these remains occur in matted masses may be seen 

 among the Sertularidte any day, but I am not aware that any such great grega- 

 rious assemblages of the Polyzoa occurs, at least among our recent species of 

 this form. This is, however, an argument of little moment. The places 

 in which it occurred also appear to have been similar to those in which Sertu- 

 larida3 of our day most love to dwell. 



We shall next proceed to the consideration of the characters of the genus. 



Mode of Occurrence and Generalities concerning Genus. 



The species described by Forbes are so dissimilar in 

 appearance that it is questionable whether it would not 

 be more convenient to place them under separate genera, 

 especially as there is a second type like Old. antiqua, 

 which I propose to describe as distinct; Old. antiqua 

 (Fig. 2), and the undescribed form, for which I propose 

 the provisional name of " discreta," being furnished with ~ ' 



a distinct axis, from either side of which alternating fans „f oMhaml "antiqua, exhibit- 

 of branches arise at regular intervals ; while Old.radiata ing enlarged summits of bramh- 

 (Fig. 3) is destitute of any central axis — its mode of ^^' ^^^ 

 growth irregular, the branches springing from a common point, so that the po- 

 lypidom, flattened from above, is stellariform more or less regularly, according 

 as the axes are equal in length or not. The radial character of this form is 

 occasionally badly marked (Fig. 4), so that it has been surmised that two 

 forms were confounded under the one name ; but in our present state of know- 

 ledge it appears unadvisable to name this variety, as it is not more distinct 



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