198 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



narrower and more numerous whorls and conspicuous spiral striae, the latter being 

 entirely absent in G. circumnodosum. 



None of the species here compared with G. circumnodosum have been found up to 

 the present time in Ireland. 



In his important paper on the " Marine Fossils from the Coal Measures of 

 Arkansas," ' J. Perrin Smith figures a specimen of Gastrioceras to which he does 

 not assign any name, but which he describes as closely resembling G. Marianum, 

 de Verneuil, in its young stage; while it is distinguished from G. Marianum in its 

 adult stage by its narrower and more highly arched whorls. It appears to me that 

 this species is intermediate in character, when mature, between G. Listen and 

 G. Marianum, and thus suggests affinities with G. circumnodosum, especially in the 

 character of its ornaments, which consist of strong tubercles on the sides of the 

 whorl ; " which on the young stages are like those of G. Marianum, but on the adult 

 form ribs reaching halfway from the umbilical shoulders to the ventral [peripheral] 

 portion of the shell." 



Mr. Perrin Smith describes G. Marianum in the same paper, giving figures of it 

 in several stages of growth, up to a diameter of 54 mm. He recognises also in 

 the same beds other " European Coal Measure forms not before known in 

 America," viz. Conocardium aliforme, J. Sowerby, and Pronorites cyclolobus, J. 

 Phillips. 



Remarks. — In the absence of the suture-line the generic position of the present 

 species has been determined in conformity with its close resemblance to well-known 

 species of Gastrioceras, especially to G. Listen, its affinities with which have just 

 been pointed out. 



The specimens upon which the present description is based are a series of empty 

 moulds crowded together upon the surface of a fragment of carbonaceous shale. 

 The weathering to which the rock has been subjected, though considerable, has not 

 been so severe as to obliterate the coarser ornaments of the shells which originally 

 occupied the moulds. Of these ornaments very distinct remains are imprinted 

 upon the concave surfaces of nearly all the moulds. By filling the latter with 

 plaster of Paris, and thus producing a cast of the surface of the slab, the form of 

 the original shell Avas reproduced, the figures 10 and 11 on PI. XLIX representing 

 two of the best preserved surfaces. The shells vary in size from 2 mm. (some 

 probably even smaller) to 31 mm., the diameter of the larger of the two specimens 

 figured. 



For the cast, which was made in the Dublin Museum of Science and Art, I am 

 indebted to the kindness of Mr. G. H. Carpenter of that museum. I was much 

 assisted further in the determination of the present species by Dr. Arthur Smith 

 Woodward, F.R.S., who very kindly had casts made for me in the British Museum 



1 'Proc. American Phil. Soc, Philadelphia,' vol. xxxv, Nov., 1896, No. 152, p. 2G2, pi. xx, fig. 1. 



