MUSEUM OF COMPARATIVE ZOOLOGY. 99 



HILDOCEKATIDU* 

 Hildocerast Hyatt. 

 Abdomen keeled and channelled. Ribs large and broad. The young 

 continue smooth throughout, first whorl. Ribs, keel, and channels appear 

 on the second whorl. The ribs are not preceded by a line of tubercles, but 

 begin as folds, bent much in the same way as in the adult, but with the ab- 

 dominal bend inclined more toward the apex. The abdominal lobe is 

 shallow and broad. Superior lateral much deeper than either the aodorm- 

 nal or inferior lateral lobes, the last named very narrow and shallow, minor 

 lobes small and pointed. 



Hildoceras bifrons Hyatt. 



Amm. bifrons Brug., Ency. Meth., Aram, No. 15. 



A mm. bifrons D'Orb., Terr. Jurass., Ceph., p. 219, pi. 5G. 



Loc. Whitby, Dumbleton, Dorsetshire, Fontaine Etoupe Fours, Poille in 

 Sarthe, Laumiere, Mende in Lozere, Verpillier, Milhaud, Plateau de Lar- 

 zac, Cesi in Umbria, Mussy pres de Semur, Chary pres de Privas, Amayer 

 sur Orne, Boll, and Metzingen ; Coll. L. de Koninck, Da*. Krantz, M. Bou- 

 cault, and Prof. Bronn. 



Hildoceras Walcotii Hyatt. 



Amm. Walcotii Sow., Min. Conch., v. 2, p. 7, pi. 106. 



Amm. Hildensis Young and Bird, Gcol. York., pi. 12, fig. 1. 



Loc. Illminster, Niort, Fontaine Etoupe Fours, Plateau de Larzac, Cesi 

 in Umbria, Milhaud, Vieux Ponts, and Guadalaviar in Aragon ; Coll. B. 

 M. Wright, Dr. Krantz, and L. de Koninck. 



Grammoceras J Hyatt. 

 Abdomen keeled, but not channelled. Whorls flattened, laterally giving 

 a discoidal aspect to the shells. Ribs finer and less prominent than those 

 of Hildoceras. The young also continue smooth much longer, and chan- 

 nels never appear ; they take, however, the same rounded form of the 

 whorl. Septa differ but slightly from Hildoceras in the higher species, 

 such as Grammoceras serpentinum ; and not all generically in the lower, 

 such as Grammoceras striatulum. 



Grammoceras striatulum Hyatt. 



Amm. striatulus Sow., Min. Conch., v. 5, p. 23, pi. 421, fig. 1. 

 Amm. Thouarsensis D'Orb, Terr. Jurass., Ceph., p. 222, pi. 57. 

 Amm. radians depressus Quens'dt, Der Jura, p. 281, pi. 40. 



* Includes all the Falciferi proper with smootV pilae. 



| Aftef St. Hilda. \ Tpa^ftrj, a line. 



