MUSEUM OF COMPARATIVE ZOOLOGY. 97 



Thysanoceras hircinum Hyatt. 

 Amm. liircinus Schlot., Pet., p. 72. 

 Amm. hircinus Quens'dt, Der Jura, p. 280, pi. 40. 



Loe. Seinur, Donau-Main Canal, and Mistlegau bei Bayreuth ; Coll. M. 

 Boucault and Prof. Bronn. 



Rhacoceras L. Agassiz. 



Rhacoceras calypso Hyatt. 



Amm. calypso D'Orb., Terr. Jurass., I., p. 167, pi. 52, figs. 7-9. 



Loc. Plateau de Larzac, Monte dc Aquasparta bei Cesi in Unibria, Mil- 

 liaud, Laumiere, Digue in Basses Alpes, and Erba bei Couio ; Coll. Dr. 

 Krantz, L. de Koninck, and Prof. Bronn. 



The abdomen is broader than in 11. heterophyllus, and the septa differ- 

 ent, but, nevertheless, the varieties of this species which are devoid of the 

 annular depressions caused by the permanent mouths, are frequently iden- 

 tified with that species. 



Ehacoceras heterophyllum L. Agassiz. 



Amm. heterophyllus Sow., Min. Conch., v. 3, p. 119, pi. 2G6. 

 Amm. heterophyllus D'Orb., Terr. Jurass., I., p. 339, pi. 109. 

 Loc. Whitby, Boll, Vassy pres d'Avallon, Erzingen (Dcp. du Doubs), 

 Balingen and Bruchsal; Coll. Dr. Krantz, M. Boucault, and Prof. Bronn. 



Rhacoceras cylindricum Hyatt. 



Amm. cylindricus De la Beche, Man. Geol., p. 275, fif. 55. 

 Loc. Schoppenstadt ; Coll. Dr. Krantz. 



Rhacoceras mimatense Hyatt. 



Amm. mimatensis D'Orb., Terr. Jurass., p. 344, pi. 110, figs. 4-6. 

 Loc. Plateau de Larzac (Dep. de l'Aveyron) and Boll ; Coll. L. de Ko- 

 ninck and Dr. Krantz. 



PHYMATOIDyE. 



Phymatoceras Hyatt. 



Phymatoceras enervatum Hyatt. 



Loc. Plateau de Larzac and Villenotte pres de Semur ; Coll. Dr. Krantz 

 and M. Boucault. 



The abdomen is much flatter in this species than in the suceeedingP.ro- 

 bustum, and in the young the channels are deeper and more distinct. The 

 increase of the radii of the spiral is also less, and there are therefore a 

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