84 The Irish Naturalist, [April. 



Scarcely less abundant than Ortlwccras in the Palaeozoic 

 seas, and as ancient in its origin was Cyrloccras, whose shell 

 has always some degree of curvature, especially in the younger 

 or apical part of it, and generally expands more rapidly than 

 that of Orthoceras. The siphuncle too, instead of forming a 

 simple tube from septum to septum, as in the latter, swells out 

 between them, looking like a string of large beads. 



Of the coiled shells there are some that closely resemble 

 the Nautilus, with which they were until recently classed. 

 They are now separated under various names which need not 

 be enumerated here. One of them,, however, is so interesting 

 and remarkable that an exception must be made in its favour. 

 Let the reader suppose that he has before him the familiar 

 form of the Nautilus shell, and that it belongs to the species 

 in which the inner whorls are not quite covered by the outer 

 ones, and hence form a deep cavity on each side of the shell 

 already described as the umbilicus. Let him further suppose 

 that the outer margin of this cavity has a thickened rim, and 

 that this rim is prolonged at the lower edge of the aperture 

 on each side of the shell into a strong flattened spine which 

 juls out at right angles to the shell, giving it quite a for- 

 midable aspect. This then with some divergences would 

 stand very well as a picture of our shell which I have called 

 in another place Aca?itho?iautihcs bispbiosus 1 in allusion to its 

 spines. The photographs (Plate 5) will give, however, abetter 

 idea of the shell than any description can do. They were taken 

 from the original, which is contained in the Museum of 

 Science and Art, Kildare-street (Annex Room III.) I was 

 under the impression at the time I wrote my description 

 of it that the specimen found at Clane was unique, but it 

 afterwards transpired that the discovery of it in Ireland had 

 been anticipated by several years by a Russian palaeontologist 

 who found a similar one in the Carboniferous rocks of the 

 neighbourhood of Moscow, but belonging, as I considered, to 

 a different species from the Irish one. This was a little dis- 

 appointing, but it added greatly to the interest of the discovery 



1 Geological Magazine, Decade 4, vol. iv , April, 189}, p. 147, "On anew 

 genus and species of Nautilus-like shell [Acanthonautilus uispiiiosus), from 

 the Carboniferous Limestone of Ireland." For the loan of the figures 

 (Plate 5), I am indebted to the kindness of my friend Dr. H. Woodward, 

 F. r.s., Keeper of Geology in the British Museum [Nat. History.') 



