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GEOLOGICAL MEMOIRS. 



bigny, &c, the Am. stellaris and Am. Scipionianus, which are evi- 

 dently in part the inner whorls, partly young specimens of A. Broohii, 

 Sow.). The genuine large Am. Bucklandi, Sow., is found much 

 more seldom in France than in the other two countries, whilst here 

 Am. bisulcatus, Brug. { — Am. rotiformis and Am. multicostatus, 

 Zieten), is more frequent. Of Am. psilonotus, Quenst., I have al- 

 ready said that I did not find it at all in France. Jules Marcou, 

 however, appears to have discovered some traces of it in Mont Jura ; 

 at all events it is extremely rare. Am. tortilis, D'Orb., commences, 

 with Am. liasicus, D'Orb., from the Arietes-str&ta,, and is a variety 

 of the same without the siphonal furrows. Am. tortus, D'Orb., is 

 the true Am. psilonotus, and, I know for certain, has not its commence- 

 ment in France. Am. oxynotus, Qu., commences in the middle of 

 the German Jurassic series, and extends through Mont Jura and 

 Burgundy as far as the Cher-Department (St. Amand), in company 

 with Am. hifer ; thence it disappears as far as France is concerned, 

 and reappears in England (Gloucester). Here, however, this Am- 

 monite is replaced by the different varieties of Am. heterophyllus, which 

 become always thicker and more considerable. The accompanying 

 Am. hifer becomes very fully developed, and has near the opening of 

 the mouth a long, projecting, tongue-like process. England appears to 

 be rich in beautiful and tolerably abundant Hippopodium ponderosum 

 and the large Avicula cygnipes ; and Lima, Pecten, and Thalassites 

 (Pachyodon) are conspicuous in beauty and perfection, more than in 

 other countries. The generally typical forms, however, in all coun- 

 tries are Thalassites and Am. angulatus for the lowermost beds, to- 

 gether with Gryphcea arcuata and the varieties of Am. Bucklandi ; 

 for the clays and limestones lying above these, Gryphcea cymbium 

 and Am. raricostatus. The last two form the transition to the fauna 

 of the middle Lias. 



II. Middle Black Jura, y. and 8. 

 Argillaceous Lias. Marlstone Series. 



Lias moyen, Lias superieur, in part. Marines a Belemnites et a Gry- 

 phcea cymbium. 

 Etage liasien (D'Orb.). 



We have certainly already found Gryphcea cymbium together 

 with Am. raricostatus ; but, lying immediately below the numis- 

 malis-cl&ys, the middle Lias must be considered as the real locality 

 of those important shells. This appears clearer in France than in 

 Swabia, especially at the east side of the elevated tract in Franconia, 

 where the Jura rocks are exposed. I do not know any place exhi- 

 biting these strata better than the village of Aschach, near Amberg. 

 It is a little retired place, entirely surrounded by post-tertiary 

 sands ; below the village, in the valley, occur the white Keuper sand- 

 stones and red clays ; upon the heights lies the coarse-grained, 

 quartoze Lias-sandstone, and above this a light-coloured lime- 

 stone bed of about 2-3 feet thick remarkably rich in fossils — Gry- 

 phcea cymbium, of 6 inches in length and 2-3 inches in breadth, is 



