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perforatum as having an apical chamber in which the breadth but 

 little exceeds the ventrodorsal diameter and doubtless at the apex 

 itself in the ananepionic substage, as in most Nautiloids, the ventro- 

 dorsal diameter exceeds the transverse. 



The coiling is so loose that the umbilical perforation is of very 

 large diameter, and the impressed zone, generated only after con- 

 tact, is very slight even on the second whorl and does not persist 

 after the whorls separate. The dorsum is, however, affected to a 

 limited extent on the free whorl in some species as shown in 

 Schroder's admirable figures. These figures give one great satisfac- 

 tion, their accuracy, size and detail being full of information. 



The whorls touch during the neanic stage only in some species, 

 Estonioceras ariense, but in others they may continue in contact 

 probably throughout the ephebic or a large part of that stage, 

 Eston. perforatum and impe7'fectum. 



The lateral angles become rounded in the ephebic stage, but there 

 is no tendency to form lateral zones or to flatten the abdomen as in 

 Falcilituites. The whorls simply become rounded, depressed ovals 

 and in the paragerontic stage the length of the transverse diame- 

 ters decrease. 



The siphuncle is fully described by Schroder in Estonioceras im- 

 perfectmn, and it is plainly ellipochoanoidal in the ephebic stage. 

 What it may be in the young has not been determined. The fun- 

 nels are very short and the connecting walls thin and long. The 

 position is subventran in the young, tending more towards the 

 centre and becoming extracentroventran in some species with the 

 advance of age. In the paranepionic substage it may again return 

 to a position nearer the venter. 



The species described by Schroder are as follows : 



Estonioceras perforatum, Schroder; Estonioceras {Lit.') lamellosum y 

 sp. His. Discoceras lamellosum as figured by Angelin et Lindstrom 

 seems quite distinct with closer coiled whorls and deeper impressed 

 zone, too deep in fact for a species of this genus,, whereas Hisin- 

 ger's figure in the Lethea suecica is a true Estonioceras. Never- 

 theless Schroder asserts that both figures were made from the same 

 "individual." Estonioceras {Lit.) heros, sp. Remele; ariense, sp. 

 Schmidt; {Lit.) imperfectum, sp. Quenstedt. 



Estonioceras muellaueri and Schroder's Estonioceras decheni have 

 been referred to the genus Falcilituites of Remele in this paper. 



