EUSTHENOCERAS HULLI. 41 



of the septate division of the shell with the body-chamber attached. The latter 

 is not quite perfect, but a fair approximation of its form and size may be arrived 

 at. The septa exhibit the closeness of arrangement characteristic of E. Hulli in 

 a similar stage of growth, and there is the same arching upwards in them upon 

 the dorsal or inner curvature of the shell (cf. PI. XIII, fig. 1 b — lower portion, 

 from the part marked a, b). 



The differences between the two species may be summed up as follows : — the 

 body-chamber is larger in proportion to the entire shell in E. Bailyi than it is in 

 E. Hulli. The septa in the former do not increase greatly in their distance apart 

 towards the body-chamber, the reverse of this being the case in the latter 

 species. The section is nearly circular throughout the shell in E. Bailyi; it 

 becomes markedly elliptical in the adult in E. Hulli. Lastly, the curvature is 

 more regular and continuous in E. Bailyi than in E. Hull!, in which it becomes 

 nearly straight at about the lower third of the shell. 



Remarks. — The great size of the individuals belonging to this species is 

 worthy of note, and did not escape de Koninck's attention in his description of 

 the species. There were giants in those days in the Carboniferous seas of the 

 British and Belgian areas; this may at least be said of the Cephalopoda, for not 

 only did Actinoceras giganteum flourish and abound, but there were also gigantic 

 forms of many of the coiled shells, such as Gcelonautilus cariniferus, Asymptoceras 

 dorsale, and others. Favourable environment, immunity from the attacks of their 

 enemies, and other physical conditions may be invoked to account for such 

 unusual development, which was most marked in the Irish area. 



Returning to the subject of these remarks, it cannot but be conceded, I think, 

 that the group to which I have given the name Eusthenoceras is transitional in 

 character between Orthoceras and Oyrtoceras ; the persistence of the characters 

 noted in Eusthenoceras in several individuals being of such a nature as to allay 

 any suspicion of their representing merely individual variations or abnormalities 

 of some kind. If this be the true interpretation of the phenomena presented by 

 these fossils, it is a further proof that the specialisation characteristic of the race 

 of the Cyrtoceratida3 met with in the Silurian and Devonian rocks was not 

 maintained in the Carboniferous period, but that, contrariwise, a series of forms 

 then appeared in which a more simple structure was the leading feature. These 

 witnessed the dying out of the race, which did not survive the close of the 

 Carboniferous period. 



I am again indebted to Prof. Joly, who lent me the fine specimen figured on 

 PI. XIII, which gives valuable information regarding the structure of the present 

 species not furnished by the other examples. 



Localities. — Oldtown, Queen's County; Rathkeale, county of Limerick. 



