EUSTHENOCERAS HULLI. 39 



ture of the shell is more regular and persistent than in E. Hulli, and the rate of 

 growth more rapid. 



If it should be found subsequently by the discovery of other specimens of 

 Eusthenoceras Baihjl that the characters found in the isolated individual described 

 persist in others, it may be necessary to modify the description of the genus as 

 given above, or to restrict it entirely to the single species E. Hulli, of which there 

 is abundant material. 



Eusthenocekas Hulli, L. G. de Koninck, sp. Plate XIII; Plate XIV, figs. 



1 a — c, 3. 



1882. Cyrtoceras Hulli, L. G. de Koninck. Annales de la Soc. Geologique de 



Belgique, torn, ix, 1881-2 (Memoires), pp. 50 — 00, 

 pi. vi, figs. 1 — 3. 



Description. — Shell elongate, of robust habit, sharply curved in the young, 

 but becoming straight in the adult. Upon a chord of 45 mm. subtending the 

 concave or dorsal side of the apical part of the shell, the greatest curvature is 

 9 mm. The section is nearly circular in the young shell, but becomes ellipsoidal 

 in the adult, the ratio of the ventro-dorsal to the transverse diameter in an 

 uncompressed specimen (Oldtown) being as 48 : 43. Body-chamber (PI. XIII, 

 fig. 1 a) not quite complete anteriorly, having a length of 150 mm. as compared 

 with 450 mm. for that of the entire shell, exclusive of the apical part, not 

 preserved in the specimen measured, or in the ratio of 1 to 3. Sutures compara- 

 tively close-set in the young shell, varying little in the distance separating them 

 until a certain stage of growth is reached, when they suddenly widen, and 

 continue to do so till the body-chamber is reached. In one of the specimens 

 (PI. XIII, figs. 1 a, 1 b) the sutures are 10 mm. apart where the greater diameter 

 of the shell is 47 mm., and where this has increased to 65 mm. the sutures are 

 20 mm. distant from each other. It may be added that in two adjacent 

 chambers, which are respectively the fifth and sixth from the body-chamber, the 

 space between the sutures augments from 16 mm. to 25 mm., the latter width, or 

 very near it, being maintained up to the penultimate chamber, the last chamber 

 being, as usual, somewhat shallower — 21 mm. (PI. XIII, figs. 1 a, 1 b). 



The direction of the sutures varies with the age of the shell ; in the young 

 they are nearly horizontal ; at a later stage of growth they become distinctly 

 arched (PI. XIII, fig. 1 c) on the dorsal (concave) aspect, passing obliquely over 

 the sides and maintaining the horizontal direction of the young shell on the 



7 



