﻿461 



the flat zone being narrower than the transverse diameters imme- 

 diately internal to this. This may be due to compression, since on 

 the septate portion the lateral curve from the abdomen to the um- 

 bilical shoulders show the somewhat flattened aspect given in 

 Saemann's figure. The umbilical shoulders are rounded. The 

 abdomen not so broad as the dorsum, that is not so broad as the 

 transverse diameter through the umbilical shoulders. 



The cast shows faint broad fold-like costations bending apically 

 which were more prominent on the shell, as is shown by other speci- 

 mens from the same locality. Saemann's figure is correct in outline 

 and proportions, but it is incorrect in that it does not give the 

 sutures which are apparent on the original, and it also brings the 

 cast of the whorls in close contact, whereas these are separated by 

 the thick dorsal and ventral shell layers. The whole surface of the 

 cast is also erroneously given, since it is marked by obscure costa- 

 tions, which must have been more prominent upon the exterior of 

 the shell. These are more prominent in the young than upon the 

 full-grown whorls. The sutures have well-marked ventral and dor- 

 sal lobes and lateral lobes with saddles at the abdominal angles and 

 umbilical shoulders. The sutures are numerous and close together 

 as in most species of this group and in Trocholites. 



The siphuncle is nearer the dorsum than that given in Fig. ic. 



The apex is smaller than in the original of Figs, ic and id, and 

 the umbilical perforation smaller and the rate of increase by growth 

 less, so that the species is smaller than Saemanni. 



The living chamber in angulatus is free as figured by Saemann on 

 the outer part only. In the original of Fig. \c-d it is free for 

 nearly the entire length. 



The prominent costae of the true Disc, antiquissimum are not 

 present in this shell nor in its allies, and the differences in form are 

 supplemented by the close coiling of the living chamber in antiquis- 

 simum. 



Saemann's original is 91 mm. in diameter, and has somewhat 

 more than three and a half volutions. The living chamber measured 

 along the median lateral line is 53 mm. in length from aperture to 

 suture. The transverse diameter of the septal floor is 26.5 mm., 

 the dorso-ventral diameter in median plane is 20.5, both without the 

 shell. The aperture is narrower in proportion to the ventro-dorsal 

 diameter, owing to the flaring of the lips and the slight constriction. 

 Only one-half is preserved and it is slightly distorted \ it may be a 



