482 THE LIAS AMMONITES. 



museum, when searching for another Ammonite. The fossil is one of the finest examples 

 of this grand species extant, and shows the remarkable flattening-in of the spiral margin 

 of the whorl where it encircles the umbilicus ; the same specific character is displayed 

 even more perfectly in the beautiful little mould of this species figured in PL LXXIV, 

 figs. 3 — 5. The Earl of Enniskillen's specimen was not known to me when PI. LXXIV 

 was drawn, and the German mould being at that time the best example I could figure, 

 it was given as a type. My description of the species had been written for a consider- 

 able time before this giant Lytoceras Jurense was found, so that I was unable to do 

 more than give the reference to PI. LXXIV on p. 413. 



Amaltheus lenticularis, Young and Bird. PI. LXXXII, figs. 14 and 15. 



Ammonites lenticulabis, Young and Bird. Geol. Surv. Yorkshire, p. 269, 1828. 



— — Simpson. Monogr. on Ammonites, p. 37, 1843. 



— — — Fossils of Torksh. Lias, p. 79, 1855. 

 Amaltheus Engelhardtii, Tate and Blake. Yorkshire Lias, p. 294, 1876. 



Diagnosis. — Shell much compressed ; inner whorls nearly concealed, outer whorl one 

 half the diameter of the disc ; sides slightly convex ; siphonal area very thin, forming 

 a sharp, feebly crenulated edge at the border ; umbilicus narrow, with upright walls ; sides 

 covered with fine transverse striae, slightly bent ; beneath the transverse radii four or 

 five longitudinal obsolete lines ; aperture narrow and acutely triangular. 



Dimensions. — Transverse diameter 73 millimetres; height of aperture 40 millimetres; 

 transverse diameter at base 12 millimetres; width of umbilicus 13 millimetres. 



Description. — The rare example of Amaltheus lenticularis, Young, now for the first 

 time figured, shows very clearly the flat, involute, obsoletely-radiated, longitudinally- 

 striated, sharp-pointed character of the species, which is a rare form in the Yorkshire 

 Lias and of which Mr. Young 1 says : — " The last shell of this family which we shall name 

 is more lenticular than any that we have seen. The exterior part 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. This rare species, found 

 in the Lias bands, may fitly be termed Ammonites lenticularis." The authors of the 

 ' Yorkshire Lias ' regard this Ammonite as a form of Amaltheus Ungelhardti, but with this 

 view I cannot agree. 



The beautiful specimen I have figured was presented by my old friend, the late Mr. 



1 'Geological Survey of the Yorkshire Coast,' 2nd ed., pp. 268, 269, 1828. 



