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broad, shallow lobes, but in some specimens the sutures are nearly 

 straight or may retain slight saddles on the venter. 

 The siphuncle is extracentrodorsan. 



Nephriticeras cavum. 



Nautilus cavus (Pal. N Y, v, Pt. ii, PI. cvi). 



The fragment of the neanic stage, figured by Hall, has the 

 nephritic whorl and similar sutures to the full grown of Nephritice- 

 ras bucinum, but the dorsal lobes are deeper perhaps and more 

 V-shaped. The septa are different in being much more widely sep- 

 arated, but are otherwise similar to those of the later stages in 

 Nephriticeras bucinum. I find in my notes that the impressed 

 zone occurs after the dorsal lobes are formed and at an earlier stage 

 than in bucinum. 



Siphuncle is unknown. 



Nephriticeras acr^eum. 



Nautilus acr^eus, Hall (Pal. N Y, v, Suppl., PL cix). 



The fragment of the neanic stage, figured by Hall, shows the 

 nephritic outline impressed zone and ridges similar to those of the 

 older stages of Nephriticeras bucinum occurring at an earlier stage 

 than they do in Nephriticeras cavum* 



Nephriticeras magister. 



Nautilus magister, Hall (Pal. N Y., v, Pis. lxii, cvii, cviiij. 



The large fossils of this species which I have examined have not 

 afforded me any information with regard to the young, but the 

 nephritic form of the whorl, the impressed zone and large beaded 

 siphuncle dorsad of the centre show that the species belongs in the 

 same genus with Nephriticeras bucinum. 



This species may have either slight ventral lobes or saddles on 

 the venter. 



Nephriticeras maximum. 



Nautilus maximus, Hall (Pal. N Y, v, Pt. ii, Pis. lxxiii, lxxiv). 



This is like Nephriticeras magister, known only through large 



fossils, but the young of the specimen figured by Hall on PI. lxxiii 



* I regret very much that in finishing this paper I have had no opportunity to revisit 

 Prof. Hall's collection and study again his old and new materials. It is not improbable 

 that his fine series of Kephriticeran species may show - that the impressed zone was pres- 

 ent as a dorsal furrow in the paranepionic substage of some of the more involute and 

 tachygenic shells. 



