Hyatt.] 284 [April 4, 



tetragonum, D'Arch. et Vern., Trans. Geol. Soc. Lond. Vol. 6, 

 pi. 30, has young which are identical with adults of Temnocheilus, 

 and adults similar to those of typical Centroceras, but less com- 

 pressed. Type, Cent. (Disc.) Marcellense sp. Hall, Nat. Hist. 

 N. Y., Yol. 5, pt. 2, pi. 65, 109. Mus. Geol. Surv., Albany. 



Butoceratidae. 



Species in this family have exceedingly rough shells. The pro- 

 jecting lips of the apertures are more or less permanent and often 

 form ridges, or lines of projecting spines or nodes. These may 

 be indefinite in number, but there is a general tendency to reduce 

 them to three rows on either side, and, if carried farther, to one 

 line along the edge of the venter. Sutures have saddles on the 

 venter. Siphon is ventral, or near venter. 



Zittelloceras, 1 nobis, includes species of arcuate Silurian and 

 Devonian longicones with whorl in section elliptical and an exter- 

 nal frilled layer resembling Dawsonoceras, but no costae, and 

 much larger ventral sinus in the aperture, and corresponding 

 deflections of the frilled ridges and lines of growth. Siphon is 

 small, tubular, and ventral. Sutures have ventral saddles, lateral 

 lobes, and dorsal saddles. The living chambers are long, and 

 apertures open. Type, Zitt. (Cyrt.) lamellosum, sp. Hall, Nat. 

 Hist. N. Y., Vol. 1, pi. 41. Amer. Mus., N. Y. 



Halloceras, 2 nobis, is confined to the Devonian. The shells 

 have similar frilled layer, flaring lips to the apertures, etc., as in 

 Zittelloceras, but the forms are Gyroceran, or nautilian. The 

 whorl is subtriangular in section. The abdomen is broad, the 

 sides divergent, and the dorsum forms the narrow apex of the 

 section. Thick costae, or rather large nodes are formed along the 

 angles of the sides in the adults. The sutures have ventral and 

 lateral lobes, and in the impressed zone, when this occurs, there 

 may be a corresponding shallow dorsal lobe. The siphon is small, 

 and near the venter. The young are identical with the adults 

 of Zittelloceras. Type, Halloceras (Gyr.) undulatum sp. Hall, 

 Nat. Hist., N. Y., Yol. 5, pt. 2, pi. 53, 54. Mus. Geol. Surv. 

 Albany. 



i Dedicated to Prof. Karl Zittel of Munich. 

 2 Dedicated to Prof. James Hall of Albany. 



