MUSEUM OF COMPARATIVE ZOOLOGY. 81 



Microceras mixtum Hvatt. 



Amm. polymorphus mizlus QuensMt, Der Jura, p. 128, pi. 15, fig. 12. 



Loc. Gloucester ; Coll. L. de Koninck. 



Is not the same as polymorphus mixtus Quens'dt, Die Ceph., p. 87, pi. 4, 

 fig. 10. This has a keel and must be of a different genus from the speci- 

 mens here described, which appear to be identical with the figure in " Der 

 Jura," as quoted above. 



DEEOCEEATIDiE.* 

 Derocerast Hyatt. 

 "Whorl circular ; pilte depressed ; linear between and bifurcated on the 

 tubercles. Tubercles large, prominent, pointed, and in a single row. 

 Septal lobes with numerous pointed, deeply cut, irregularly shaped minor 

 lobes. Abdominal lobe very deep, and level with superior lateral lobe. 

 Siphonal cell long and narrow. 



Deroceras ziphius Hvatt. 



Amm. ziphius Ziet., Verst. Wurt., p. 6, pi. 5, fig. 2. 



A mm. arnatus sparsinodus Quens'dt, Die Ceph., p. 82, pi. 4, fig. 5. 



Amm. ziphius Quens'dt, Der Jura, p. 5)7, pi. 12, fig. 2. 



Loc. Loppingen ; Cull. Mus. of Stuttgart. 



Note. The foregoing descriptions of the Discoceratidse, Liparoceratid.-e, and Dero- 

 ceratidse comprehend all the species in the Museum collections from the Lower Lias, 

 except Amm. Birchii Sow., which I was unable to assign to its proper place. 



Middle Lias. 

 LIPAROCERATID^I. 



There is throughout the three genera of this family a positive agreement 

 in the septa and the mode of development. 



The young of Liparoceras indecisus resemble the adult of ^4 ndrogynoce- 

 ras, and the young of Androgynoceras Tn turn closely resemble the adults 

 of Microceras. 



Abdominal lobe is large and not generally so deep, but of less width than 

 the superior lateral. Inferior lateral lobe very narrow, and of insignificant 

 size ; one auxiliary lobe is usually visible on the side. The minor lobes 

 are particularly sharp or pointed ; penetrate deeply into the cells. Both 

 cells and lobes unequally divided by three minor lobes. 



Microceras. 



Microceras planicosta Hyatt. 



Amm. planicosta Sow., Min. Conch., v. 1, p. 1C7, pi. 73. 



* Includes the Dorsati. f Ae'pas, skin. 



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