86 BULLETIN OF THE 



and mo«t prominent, divided on the abdomen. The young are smooth for 

 the first two of three whorls ; tubercles occupy the whole next whorl, ex- 

 tending gradually into tuberculated pilse between which the smooth pilaj 

 finally appear. Abdominal lobe larger and deeper than superior lateral 

 lobe. Inferior lateral lobe small, shallow ; both unequally divided. Su- 

 perior lateral cell entirely on the abdomen. Inferior lateral cell on the 

 side. 



THYSANOID^J. 

 This family includes the Fimbriati, Ligati, and Heterophylli, which 

 agree in the foliaceous character of the septa. 



Thysanoceras.* 



Abdomen rounded ; whorls exposed ; the envelopment does not extend 

 laterally over mure than one third of each interior whorl. 



Abdominal lobe about the same depth, but narrower than the superior 

 lateral lobe: the latter is equally divided by a peculiar minor cell of a lobi- 

 form aspect. The siphonal cell is cuneiform, and the superior and inferior 

 lateral cells equally divided. 



Thysanoceras flmbriatum Hyatt. 



Amm. fimbrialus Sow., Min. Conch., v. 1, p. 145, pi. 164. 



Amm. fimbriates D'Orb., Ten-. Jurass., Ceph., p. 313, pi. 98. 



Amm. fimbriates Bronn, Lcth. Geog., p. 441, pi. '2:3, fig. 2. 



Loc. Lyme Regis, Semur, Plateau de Larzac, Milhaud, Dep. de l'Avey- 

 ron, Balingen, Gundershofen, Schombcrg, Falkenhagen, Lippe, and Sondel- 

 fingen ; Coll. Mus. of Stuttgart, B. M. Wright, M. Boucault, Dr. Krantz, 

 L. de Koninck, and Prof. Bronn. 



Rhacocerast Aoassiz. 



Abdomen rounded ; sides of the whorls flattened : envelopment extends 

 about two thirds over each of the interior whorls, or entirely encloses them, 

 covering up the umbilicus. 



The lobes and cells gradually decrease in size inwardly, and are remark- 

 able tin- the profusion and peculiar foliaceous aspect of the minor cells. 



Rhacoeeras Loscombi Hyatt. 



Amm. Loscombi Sow., Min. Conch., v. 1, p. 183, pi. 183. 

 Amm. heterophyllus numismalU Quens'dt, Die Ceph., p. 100, pi. 6, fig. 5. 

 Amm. Loscombi D'Orb., Terr. Jurass., Ceph., p. 262, pi. 75. 

 Loc. Lyme Regis and Semur; Coll. Damon, Wright, Boucault, and L 

 de Koninck. 



* Qvvavos, fringe. t I'ukos-, r- < I. 



