AMALTHEUS ENGELHARDTI. 401 



■this character, which, however, is fairly shown in portions of the fine specimen figured 

 in PI. LXX. The shell is extremely involute, and has a much smaller umbilicus than 

 its associated species, A7na!. margaritatus, with which in other respects Amal. Engelliardli 

 stands in very close relationship. The siphonal area is very narrow forming a sharp keel, the 

 margin of which is in general smoothly rounded and sometimes obscurely crenated ; the 

 spire is composed of very compressed whorls, which become thinly flattened away towards 

 the siphonal area, and thickened near the umbilicus, around which they present an obliquely 

 truncated wall ; the aperture is high, oblongo-lanceolate, narrow, and compressed, its sides 

 form an acute angle, rounded internally, where it embraces three fourths of the penultimate 

 whorl. The suture-line is extremely complicated, forming a number of extremely minutely 

 divided lobes, and in this respect differing from the suture-line of Amal. margaritatus (PI. 

 LIII). By taking an impression of one of these my artist has been enabled to give a very 

 accurate delineation of the sutural outline, which he has placed in situ on the figure, and 

 -which is now drawn for the first time. Of this structure d'Orbigny said, " Je n'ai pu les 

 apercevoir assez pour les dessiner et les decrire." The siphonal lobe is large and composed 

 of several long lateral branches. The siphonal saddle is wide and terminates in small narrow 

 folioles. The principal lobe is very large, it has a long, terminal, ramified stem in the 

 centre, and three lateral ramified stems on each side, all of which are highly digitated. 

 The lateral saddle is much smaller than the siphonal saddle, and terminates in six narrow 

 folioles. The internal lateral lobe is much smaller than the principal lateral, and consists 

 of a central stem terminating in a trifurcation, with two divided branches on each side of 

 the central stem. The auxiliary lobes are small, with delicate pointed ramifications, and 

 the auxiliary saddles terminate in minute rounded folioles ; the sutural-lines are so closely 

 approximated on the sides of the mould in consequence of the narrowness of the chambers 

 that they present an inextricable labyrinth to the student, and require a most careful 

 study in order to follow them out through all their windings. 



I have not seen a young shell of this species, nor had d'Orbigny, but he felt assiu"ed that 

 it presented the same characters throughout at all ages, and that it was not an adult variety 

 of Amal. margaritatus. Young and Bird^ described an Ammonite under the name A. 

 lenticularis, which appears to be identical with Amal. UngelUardti. They say "the exterior of 

 the whorl runs to a thin edge, plain, or very faintly crenated; the sides are smooth or marked 

 with very faint undulating lines ; the central part is an umbilicus, with upright sides, the 

 inner whorls being scarcely visible and the aperture forms a triangle, of which the outer 

 angle is extremely acute, owing to the thinness of the edge." Mr. Simpson^ has described 

 A. reticularis, which agrees so well with Amal. Engelhardti that, in the absence of figure, or 

 specimen, his diagnosis may be considered identical. " Volutions five, inner ones more than 

 three fourths concealed ; outer whorl one half the diameter, most convex on the outer half. 

 Transverse striae numerous, fine, waving, crossing ; numerous fine, longitudinal striee ; keel 



1 'Geological Survey of the Yorkshire Coast,' 2nd ed., p. 269, 1828. 



2 'Fossils of the Yorkshire Lias,' p. 78, 1855. 



52 



