70 CARBONll^KROUS CEPHALOPODA OP IRELAND. 



much less de(;ply channelled periphery, in the crennlated character of the orna- 

 mentation of the inner whorls, and finally in its less compressed form. 



It also resembles A. discoideum, de Kon., sp., but it tapers more rapidly, has 

 much more numerous ridges, a less deeply channelled periphery, and the first 

 whorl free. The sides also in A. hibernicitm are more strongly convergent 

 towards the poripliery than those of A. discoideum, or, in other words, the latter 

 has a more compressed shape. 



EemarJcs. — This shell has been met with, up to the present time, only in the 

 quarries at St. Doulagh's, where it is tolerably abundant. It is easily dis- 

 tinguished, even in fragments, from A. mutabile by its less compressed form and 

 less deeply channelled periphery. In the young shell the first whorl being out of 

 contact with the succeeding one is a distinctive feature. 



A cast of the body-chamber shows at the base very distinct impressions of the 

 shell-muscle as well as indistinct marks of the " Runzelschicht " (or " wrinkle 

 layer;" marks supposed to represent the surface of the mantle of the animal). 

 The former consist of two incised lines which are 3 mm. apart on the sides 

 of the shell, getting gradually nearer towards the angles of the whorl. They 

 follow in their course the contour of the last septum, whose outline is also 

 impressed, rather faintly, upon the cast. There is also a series of short longi- 

 tudinal indentations, crowded together, on the dorsal area situated in advance of, 

 but almost touching, the incised lines of the shell-muscle. These have precisely 

 the appearance produced by impressions of the thumb-nail when lightly applied 

 to a soft substance, such as modelling wax. They doubtless served to strengthen 

 the hold of the muscle to the shell, and recall similar points of attachment 

 observed in CmlonantUus,^ as well as in the recent Nautilus. 



Locality. — St. Doulagh's, county of Dublin. 



Apheleceras trochlea, F. M'Coi/, sp. 



1844. Nautilus (Discites) tbochlua, F. 31'Coi/. Synop. Carb. Foss. Ireland, 



p. 19, pi. iii, fig. 4. 

 185o. — — — — British Palaeozoic Foss. ,Fa8c. 



iii, p. 561, pi. iii h, fig. 16. 

 1878. — TKOCIILEA, L. G. de Koninck. Faune Cale. Carb. Belgique 



(Ann. Mua. Eoy. d'Hist. Nat. Belgique, Paleont., 

 torn, ii), pt. 1, p. 119, pi. xxvi, fig. 4. 

 1893. Apheleceuas tuochlea, A. Hyatt. Carboniferous Ceplialopods. Second 



paper. Geological Survey of Texas, Fourth 

 Annual Eeport, 1892, p. 414. 



^ ' Cat. Foss. Cepb. British Museum,' pt. 2, 1891, p. 106, tig. 15. 



