396 THE LIAS AMMONITES. 



ornamented with three points, of which the inferior one is bifurcated. The siphoiial 

 saddle is as wide as the principal lateral lobe, and terminates in five rounded leaves 

 resembling palettes. The principal lateral lobe is formed of five branches, of which the 

 large terminal one is trilobed. The lateral saddle, as wide as the principal lateral lobe, 

 is composed of six leaves rounded like those in the siphonal saddle. The lower lateral 

 lobe, one third smaller than the principal lateral, is ornamented also with five unequal 

 branches. The other lobes gradually diminish in length and ornamentation as they 

 approach the umbilicus." 



Professor d'Orbigny appears to have had more than 100 specimens of this Ammonite 

 before him for comparison, and from his study of these varied forms at different ages has 

 made the following observations.^ " This species is without contradiction one of the 

 most singular in its varieties of age. Up to a diameter of 7 millimetres it is smooth, 

 with a round inflated margin ; its whorls are narrow, and frequently marked with deep 

 furrows, which pass over the siphonal area ; these furrows suddenly cease at this period 

 of growth, the whorls become flattened and enlarged, and almost carinated on the 

 siphonal area; they remain thus more or less for some time according to the individuals, 

 and then commence to assume some lateral undulations. The nodosities on the back, 

 and all the external ornaments, only usually show themselves when the shell attains 

 about 20 millimetres in diameter, then the nodosities increase in size with the growth, 

 whilst the radiating ribs of the sides appear, on the contrary, to become attenuated up 

 to the greatest diameter of which we have knowledge. Among the large number of 

 specimens that I have had the opportunity of comparing, I have found one remarkable 

 variety having closer lateral ribs, with the knobs on the back at least three times as 

 numerous as in the other specimens." 



Affinities and Differences. — This Ammonite has few affinities in structure with its 

 congeners, the large nodosities formed in the siphonal area by the rib-like structure that 

 develop these, liken it to Amaltheus margarilatus ; it is readily distinguished from that 

 species by the greater width of the area, by its being more obtuse, and provided wuth 

 much larger and fewer tubercles than are found in Amal. margaritatus. In early age the 

 shell is without lateral spines, and the lobe-line much less complicated than in Amal. 

 margaritatus. 



Locality and Stratigrapliical Position. — I have collected this Ammonite in nodules of 

 ochreous Middle Lias from brick pits at Hewletts Hill, Southam, and Leckhampton, 

 Gloucestershire ; and Mr. Beesley records it from the Jamesoni Beds at Fenny Compton, 

 Warwickshire. In France it has been collected from the Middle Lias at Coutards, Vallee 

 de Saint-Pierre, pres de Saint-Amand, Cher, Fresnay-le-Puceux, Calvados. 



In Germany this shell is found in Swabia associated with Aeg. Maugenesti, Aeg.^ 

 hipunctatum^ Aeg. centaurus, and Aeg. Valdani. 



^ ' Paleontologie Frangaise Terr. Jurassique,' torn, i, pp. 252 and 263. 



