274 peof. w. jr. sollas on ichnittm [May 1900,. 



The rocks which have furnished Oldhamia in Ireland have always 

 been regarded as belonging either to the Cambrian or to some 

 still more ancient system ; but the observations of Mr. MacHenry,. 

 according to whom Oldhamia occurs in Wexford in intimate 

 association with Ordovician fossils, have suggested doubts on this 

 point. 



In America, according to Barrois, a form of Oldhamia is said to 

 occur plentifully in the Potsdam Sandstone (Upper Cambrian) of 

 Wisconsin. 



No instance is recorded of Oldhamia from strata of later age 

 than the Ordovician, and I have never myself met with any 

 markings comparable to Oldhamia in rocks younger than those of 

 Bray Head ; this comparatively narrow restriction in time, not- 

 withstanding a wide distribution in space, is a very noticeable fact,, 

 and should be carefully borne in mind in discussions as to the 

 origin of Oldhamia. 



The genus Oldhamia was defined by E. Forbes (2), who re- 

 cognized two species, 0. radiata and 0. antiqua. Later J. R. 

 Kinahan (3) added a third species, which has not been generally 

 accepted ; Baily (6) speaks of it as a mere variety of 0. radiata. 

 Goppert (5) regarded the distinction between the two species 

 of Forbes as of generic value, and, while retaining 0. radiata as the 

 designation of one, renamed the other Murchisonites Forbesi. In 

 this procedure he has not been followed by other investigators. 

 The species 0. Hovelaquei, described by Barrois (23), differs in 

 several respects from either of those found at Bray. It is larger, 

 and consists of a definite number of processes (twelve) having a 

 flabellate arrangement, inserted independently at the same part of 

 a stem, which is slightly swollen to receive them ; this stem pro- 

 ceeds from another, which is similar but slightly longer ; a whorl 

 of appendages, such as occurs in 0. antiqua at the point of branch- 

 ing of the stem, is not present in 0. Hovelaquei. The appendages 

 are semicylindrical, simple, smooth, and obtuse at the end, 20 mm. 

 in length and 1 mm. in breadth. The stem from which they 

 proceed is 20 mm. in length, and only slightly thicker than the 

 appendages. 



A specimen of the new fossil, Ichnium Wattsii, to be presently 

 described, is classed with 0. radiata in the collection of the 

 Geological Survey of Ireland. 



The organic nature of Oldhamia was scarcely a matter for doubt 

 in the minds of the earlier writers ; it was described by its 

 discoverer (1) as ■ small zoophytic markings, which do not appear 

 to be referable to known genera.' Great diversity of opinion, 

 however, marks the attempts to assign to it a definite place in the 

 organic world ; thus Forbes (2), while noticing its resemblance to 

 Sertularian zoophytes or polyzoa;, concludes by allying it with 

 the Tunicata ; J. R. Kinahan (3), to whom we are indebted for the 

 fullest and most accurate description of Oldhamia, confidently 



