250 R. Biillen Newton — On Archanodon Jiikesi. 



and almost incapable of proper definition, although the anterior 

 adductor muscle impression is seen to be situated just beneath the 

 upper margin of the shell, anteriorly and close to the umbone \ 

 surface ornamented at intervals with bold concentric growth-lines. 



Dimensions. — Length, 140 mm.; height, 54 mm.; diameter 

 (allowing for closed valves), 34 mm. 



Remarks. — The privilege has been accorded the writer by- 

 Mr. J. Nolan, of the Geological Survey of Ireland, of examining 

 the original specimen from Kiltorcan, to which Forbes gave the 

 provisional name of Anodon Jukesi, and which Baily at a later date 

 described and figured as Anodonta Jukesi. This type, as well a& 

 other examples of the shell from the same locality, has sufi"ered more 

 or less from lateral compression during the period of fossilization, so 

 that the valves are much flattened and shallow, differing in this 

 respect from the beautiful convex form of the species as exhibited in 

 the sandstone impressions from Monmouthshire. Somewhat similar 

 conditions have affected the valves of the closely allied species^ 

 Amnigenia {Gypricardites) Catskillensis,^ the only mollusc found in 

 the Oneonta Sandstone (= Upper Old Eed Sandstone) of ChenangO' 

 Co., New York State, and Hall's remarks in connection therewith 

 are of interest to quote : " The various phases of this species seem. 

 to be all due to the degree and direction of pressure during the- 

 process of embedding " (Palgeontology ; Lamellibranchiata : Geol. 

 Surv. State New York, 1885, p. 517). 



Another fact of interest regarding the valves from Monmouth- 

 shire is their association with fish remains,^ although only in a 

 comminuted state and quite beyond determination. 



In Ireland the mollusc occurs with Palceoj^teris Hibernica, etc.,. 

 Coccosteus, etc., and Eurypterns Scoideri ?, etc. ; in Northumberland 

 with Ulodendron ornatissimum and Catamites ; and in America 

 A. Catshillensis, the close ally of the British species, is found in 

 company with plant and fish remains (Holonema rugosum).^ 



All these facts demonstrate that the genus Archanodon was of 

 lacustrine or fluviatile origin, and that the deposition of the beds 

 containing it, whether in England, Ireland, or America, must have 

 been regulated by similar physical conditions and in close proximity 

 to land. A good deal of discussion has transpired as to whether 

 these Upper Old Eed Sandstone rocks should be regarded as Upper 

 Devonian or Lower Carboniferous, and it is hoped that the 

 Geological Survey Memoir now in progress on the Monmouthshire- 

 neighbourhood may finally determine this point. 



Notwithstanding its intimate relations with the Anodonta of 

 modern times, there can be no doubt as to the desirability of 

 recognizing Mr. Howse's name of Archanodon for this ancient 

 species, although it has been so singularly overlooked by palaeon- 

 tologists. Its adoption will necessitate the extinction of AmnigeniO' 



1 Examples of this mollusc are exhibited in the Geological Department of the- 

 British Museum. 



* On the authority of Mr. A. Smith "Woodward. 



3 See Dana's " Manual of Geology," 1895, ed. 4, p. 618. 



