412 THE LIAS AMMONITES. 



The sutural line is extremely tortuous and followed with much difficulty ; it forms 

 three lobes and three saddles and some accessory parts. The siphonal saddle is smaller than 

 the principal lateral lobe, and divides into two branches, each of which terminates in trifid 

 folioles. The siphonal lobe is much smaller than the principal lateral, and formed of two 

 nearly equal parts deeply divided in the middle. The principal lateral lobe forms two large, 

 highly- ramified branches (PI. LXXIII, fig. 3), which arise from a multibranched stem. 

 The outer lateral saddle is much smaller than the superior lateral lobe, its central stem 

 divides into two trifid folioles, with a central stem dividing them (fig. 3). The inner lateral 

 lobe is not half the size of the principal lateral, and its stem, with lateral twigs, divides into 

 two nearly equal-sized trifid terminal branches. The auxiliary saddle terminates in three 

 folioles, and the auxiliary lobe is very short and divides into two long branches. 



The late Professor A.'d'Orbigny had an opportunity of studying some young forms of 

 the shell, and his observation amounts to this that Lyt. cornucopia is very variable in 

 form according to the different states of conservation in which it is found, and the precise 

 age when it is examined ; a shell of the diameter of 25 to 30 millimetres is ornamented 

 with striae united into fasciculi, and each is separated from the other by a furrow. 

 Like Lyt. fimhriatum it has, according to the age of the individual, prominent undulating 

 fimbriated ribs. When the external layer of the shell exists there are small ribs with 

 very prominent festoons ; when this layer is wanting the inner layer still retains feeble 

 impressions, the mould, however, only shows a surface altogether smooth. 



Affinities and Differences. — This species is closely related to Lyt. fimhriatum, it has 

 the rounded whorls, prominent ribs, and fimbriated margin of that species, but the 

 whorls are larger and more evolute, and the lobes and saddles are somewhat diff'erent. 



Locality and StratigrajpUcal Position. — This Ammonite is collected from the Upper 

 Lias with Ilarpoceras serpentinum at Whitby and Runswick, and with Stephanoceras 

 annulatum, according to Prof. Blake, at Millington, Yorkshire. I have not met with it 

 in the Midland Counties, nor in any collection of Upper-Lias fossils derived from this 

 region, so conclude it is a rare form in the Midland district. 



Foreign Distribution. — Professor d'Orbigny enumerates Ligny, near Lyon; Muhlhausen, 

 Gundershofen, Bas-Rhin ; Mende, Lozere ; Fressac, Gard ; Belvedere pres de St. Amand, 

 Cher ; Clapier, Aveyron ; Charolles, Saone-et-Loire. 



Monsieur Dumortier ^ says A. cornucopia " is one of the most persistent and most 

 important fossils of the zone ; it is accompanied throughout by A. bifrons, and is 

 recognised of all sizes. The mines of Verpilliere have yielded a great number of very 

 beautiful specimens (PI. LXXIII an example), some of these were 400 millimetres in 

 diameter. The test is well preserved, and does not appear to have suffered the least 

 alteration in its form." 



^ * Etudes Pal coot, sur les Depots Jurassiques du Bassiu du Rhone,' torn, iv, p. 113, 18/4. 



