42 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



Eusthenooeeas Bailyi, L. G. de Koninch, sp. Plate XIV, figs. 2 a, 2 1>. 



1882. Ctbtoceras Bailyi, L. G. de Koninch. Annales de la Soc. Geologique de 



Belgique, torn, ix, 1881-2 (Memoires), pp. 50— GO, 

 pi. v, fig. 1. 



Description. — Shell (the only example known) of moderate size, strongly 

 curved in the apical part, but becoming straighter as the body-chamber is 

 approached. Upon a chord of 97 mm. subtending the concave side the greatest 

 curvature is 17 mm. The section is circular in the young stage of growth, and 

 does not deviate from this form in the adult. The body-chamber is of consider- 

 able length. As to its length in proportion to that of the entire shell only an 

 approximation can be come to, for part of the apex is wanting, and the body- 

 chamber itself is not perfect, but it would appear to have been nearly one-half. 



The septa are approximate and deeply concave. At a diameter of 25 mm. 

 they are 6 mm. apart ; where the diameter has increased to 38 mm. they are 10 

 ram. distant, there being an interval of about 40 mm. between the two points 

 measured. It can thus be seen that the septa increase very gradually in their 

 distance from each other. 



The sutures arch slightly forwards on the dorsal or inner curvature of the 

 shell, and become straight on the ventral aspect, a condition the reverse of what 

 is generally encountered in these curved shells (cf. Barrande, ' Syst. Sil. de la 

 Boheme,' vol. ii, pi. cli, figs. 28—30). 



The siphuncle as seen in the concavity of the last formed septum is about 

 twice its own diameter above the centre, that is towards the ventral or convex 

 side of the shell (PL XIV, fig. 2 h). 



The test is quite smooth. 



Size. — Length, measured along the outer curvature, 225 mm., of which the 

 body-chamber occupies about 100 mm. ; greatest diameter, measured near the centre 

 of the body-chamber, 56 mm., least 12 mm., the latter not far from the apex. 



Affinities. — I was at first inclined to the opinion that the present species was 

 the young of Eusthenoceras Hulli, and my doubts upon this point are not entirely 

 dispelled. One of the most marked features in E. Hulli is the extraordinary size 

 of the chambers in the adult stage of growth. Should E. Bailyi prove to be the 

 young of E. Hulli this abnormal development of the chambers could not have 

 been attained. On the other hand, the curvature of the shell in the present 

 species is much less restricted than it is in E. Hulli, giving a very different aspect 

 to the shell. Single specimens are always difficult to deal with unless they have 

 some very distinctive features, and it must be left to individual opinion to 



