84 The Irish Naturalist. April, 



Mr. Matthew discusses the relation between Monocraterion 

 and Histioderma (p. 162), the type-specimens of which are now 

 among the collections of the Geological Survey in the Dublin 

 Museum. 1 On this point, I may quote from an interesting 

 letter that I received from Mr. Matthew, dated 8th March, 

 1900. At that time we had not the advantage of discussing 

 more than the preliminary abstract of Prof. Sollas's paper, and 

 our correspondence had arisen over Histioderma. Mr. Matthew 

 wrote, "I have not noticed anything in the nature of 

 a reticulation within the burrow of Monocraterion. The 

 impressions of the supposed tentacles can however be traced 

 for some distance down the slope of the burrow along its 



sides, evidently continuous with the furrows outside 



I have seen areas of surfaces of the flags, so pitted with these 

 burrows that the tentacles would have come in contact at 

 their extremities." 



It would now be highly interesting to hear from Mr. 

 Matthew whether the internal tentacular markings run up to 

 the top of any given series of lateral and radial markings, 

 and thus across successive layers of the rock in which these 

 radial markings occur. If they do so, Prof. Sollas's ingenious 

 suggestion would not apply in their case, while the case of 

 Oldhamia might again deserve consideration. 



Prof. Sollas has accidentally passed over American work, 

 since he merely quotes Barrois for the statement that " a form 

 of Oldhamia is said to occur plentifully in the Potsdam Sand- 

 stone (Upper Cambrian) of Wisconsin," while no American 

 references occur in his otherwise admirable bibliography. A 

 short but stratigraphically important paper by Mr. C. D. 

 Walcott 2 formed the subject of a notice in the Irish Naturalist 

 for 1896 (p. 254). In that paper, Walcott discussed James 

 Hall's species Oldhamia fruticosa, from the Trenton Limestone 

 of Wisconsin, which was described in 1865. He also pointed 

 out that Lap worth 3 mentions a form of Oldhamia in Upper 

 Cambrian slates at Farnham, Province of Quebec. Lapworth, 



1 See G. A, J. Cole and J. W. Evans, letter in Geol. Mag., 1900, p. 48. 



2 " Discovery of the genus Oldhamia in America," Proc. U.S. National 

 Museum, vol. xvii., 1894, P313. 



3 Trans. R. Sac. Canada, vol. iv., 1887, section iv., pp. 180 and 183. 

 (Walcott quotes the date as 1877.) 



