MUSEUM OF COMPARATIVE ZOOLOGY. 85 



Deroeeras armatum Hyatt. 



Amm. armatus Sow., Min. Conch., v. 1, p. 215, pi. 95. 

 Loc. Lyme Regis, Dorsetshire; Coll. Damon. 



Pei'onoceras * Hyatt. 

 Abdomen depressed; pihe depressed; linear between the tubercles; usu- 

 ally, but not invariably, bifurcated by the tubercles on the sides, though in- 

 variably bifurcated on the abdomen. Tubercles depressed, often obtuse 

 upon the easts, but pointed and prominent upon the shell. Septa not 

 closely crowded as in Deroeeras, or so profusely branching. 



Peronoceras fibulatum Hyatt. 



Amm. Jibulalus Sow., Min. Conch., v. 4, p. 147, pi. 407, figs. 3, 4. 



Loc. Whitby, Boll, Plateau de Larzac, Robin Hood's Bay, St. Qucntin 

 pres de la Verpillier; Coll. Dr. Krantz, L. Agassiz, Prof. Bronn, and L. de 

 Koninck. 



Peronoceras subarmatum Hyatt. 



Amm. subarmatus Sow., Min. Conch., v. 4, p. 146, pi. 407. 



Amm. subarmatus Young and Bird, Geol. York., p. 250, pi. 13, fig. 3. 



Loc. "Whitby ; Coll. Dr. Krantz. 



Peronoceras muticum Hyatt. 



Amm. muticus D'Orb., Terr. Jurass., 1, p. 274, pi. 80. 



Loc. Semur and St. Ainand ; Coll. Boucault and L. de Koninck. 



Peronoceras nodogigas Hyatt. 



Amm. nodogigas Quens'dt, Der Jura, p. 125, pi. 15, fig. 8. 

 Loc. Goppingen ; Coll. Mus. of Stuttgart. 



Peronoceras fraudulentum Hyatt. 



Loc. Lyme Regis ; Coll. Damon. 



Abdomen rounded, and much broader than the back ; tubercles promi- 

 nent, salient ; pilas single, thick, depressed. Young resemble Planicosta, 

 having the flattened abdomen and pilre of the latter until a late period. 

 Abdominal lobe narrow and deep. Superior lateral cell narrow and 

 deeply cut by pointed minor lobes. Si phonal cell long, narrow, serrated. 



Peronoceras alternum Hyatt. 



Loc. Milhaud, De'p. de l'Aveyron ; Coll. L. de Koninck. 

 Whorls much flattened ; sides gibbous ; tubercles depressed, widely sep- 

 arated by numerous intervening smooth pihe. Tubcrculated pilae, large 



* Ilfpovr), a clasp. 



