450 



NEW YORK STATE MUSEUM 



ceratidae and the scope of none of the genera of the Cycloceratidae 

 could be extended wide enough to receive the species in question. 

 Nor are we at all sure that the family Cycloceratidae will be the 

 proper receptacle for this genus, in view of the marginal position of 

 the small orthochoanitic siphuncle and the character of the annula- 

 tions, and consider it possible that it may be a primitive member of 

 the Tarphyceratidae. Under the latter caption it is stated by Hyatt 

 [Zittel-Eastman, p. 519], " Orthoceracones represented by genera at 

 present undescribed ". This may be one of these hitherto unde- 

 scribed genera. 



The appearance of costae in several forms of the Tarphyceratidae, 

 which leads to the annular costae of the Plectoceratidae may be in 

 line with the annulations of the shell here under consideration. The 

 placing of Orygoceras with the Cycloceratidae is for these reasons 

 only provisional. 



The peculiar restriction of the annulation to the inner side of the 

 outer wall of the shell is more fully described under the type species. 

 Its bearing upon the explanation of the probable origin of annulation 

 in the cephalopod shell will be discussed in a later paper. The struc- 

 ture of the siphuncular wall shows this genus to belong to the 

 Orthochoanites. The wall like that of the Orthoceratidae is com- 

 posed of short straight septal necks and connecting sheaths. 



Orygoceras cornu-oryx Whitfield (sp.) 



Plate 14, figure 5-8 



Orthoceras cornu-oryx Whitfield. Amer. Mus. Nat. Hist. Bui. 

 1886. 1:320, pi. 27, fig. 1, 2, 6 



Description. Short, stout orthoceracone, attaining a length of 

 60+mm expanding at the rate of I mm in 5-7 mm and attaining a 

 greatest width of 20 mm. Section of conch depressed, elliptic (the 

 minor and major diameters in the ratio of 6 7), but sometimes nearly 

 circular. Outer shell thick ; smooth exteriorly but provided with in- 

 ternal ringlikc thickenings which give to the casts an annulated 

 appearance; the apparent annuli increase in strength in apertural 

 direction, are broad, flat and little elevated and separated by about 

 equally broad flat depressions ; their width increases from 2.5 to 3.5 

 mm in the specimens investigated. Living chamber large, about one 

 third the length of the whole conch. Aperture as a rule straight, 

 transverse. Cameras very shallow, there being 7 in the space of 10 

 mm in the apical phragmocone and 5 in the mature portion; sutures 

 sightly undulating, with broad shallow lateral saddles and a similar 

 antisiphonal lobe. Septa little convex, their depth about twice that 



