CCELONAUTILUS GRADUS. 59 



of the peripheral area in comparison with that of the sides is also much greater 

 than in G, planotertjatus. From C. subsulcatus, Phill. sp., the present species 

 differs in its less rapid rate of increase, closer septa, proportionately broader 

 periphery, and much larger central vacuity. 



Remarks. — The specimens which I regard as the young of the present species, 

 several of which are figured on PI. XX (figs. 5 — 9), are, I think, of considerable 

 interest. I collected about a score of them in a piece of rock of such a size 

 that it could easily be lifted. They are nearly similar in size (the largest only 

 35 mm. in diameter), several of them showing the margin of the aperture, 

 proving them to be complete individuals. The rock, a decomposing limestone, 

 easily yielded to the hammer, and thus its fossil contents were extracted with little 

 difficulty, the only drawback being that the shells were so numerous and so close 

 together that several had to be sacrificed in securing a few complete ones. 



I had some hesitation at first in deciding that these small individuals were 

 the young of Ccelonautilus gradiis, A. H. Foord, rather than an independent 

 species, but there appears to be sufficient data for this determination of tbem, 

 though I have not enough material to justify me in breaking away the older 

 whorls of G. plauotergatus, and thus exposing the complete young shell for com- 

 parison with the small shells in question. An important point in favour of my 

 view of their relationship to G. gradus consists in the presence of those peculiar 

 incipient folds which are conspicuous in that species, and to this must be added 

 the possession of a proportionally large central vacuity (cf. PI. XX, figs. 1 a and 5). 

 Furthermore, the form and proportions of the whorls in the small individuals are 

 similar to those of G. gradiis, so far as can be made oat from the exposure of the 

 inner whorls in the umbilical depression of a perfect individual, and from sections 

 of the whorls in a broken one belonging to that species. Professor Hyatt 

 regards this species as probably a member of his genus Stroboceras,^ and he 

 refers to the prominent transverse folds figured by me in the young whorls which 

 show its affinities with Trigonoceras. The folds are faint, not prominent ; the 

 figure {loc. cit., fig. 19) makes them too distinct. My own opinion is tliat it 

 belongs properly to Goelonaidilus, and I think there is good ground for this view 

 of its relationship when its general features are taken into account, and it is 

 compared with the allied forms under which I have grouped it in this Monograph. 

 Localities. — Kildare (probably Clane) ; Rathkeale and Curraghbridge, county 

 of Limerick. 



1 " Carboniferous Cepbalopods." Second paper. 'Geological Survey of Texas, Fourth Auuual 

 Eeport,' 1892 (1893), p. 411. 



