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"493/' which has also the characteristic form and markings of 

 this genus. This last has no contact furrow, according to Barrande's 

 Fig. 7, even in a late neanic substage, although there is a distinct 

 contact furrow in the ephebic stage according to his figure of the 

 full-grown shell. 



Melonoceratidce. 



Under this title, in Genera of Fossil Cephalopods, I included 

 a number of genera having special interest in this connection. The 

 impressed zone is not present in Melonoceras, which is an arcuate 

 form, and in most species of Oonoceras. 



Cranoceras, containing the only apparently arcuate form possess- 

 ing a dorsal furrow, belongs to this family and appears to be allied 

 to the more closely coiled nautilian forms Nedyceras. All of these 

 forms have subtrigonal whorls, with siphuncle ventrad of the centre. 

 The resemblance of Estonioceras and Remeleceras have led me to 

 place them also under the same family name. 



Estonioceras. 



This genus was described by Notling,* and separated from 

 Lituites, which it only remotely resembles in having some of the 

 volutions free. 



Schroder has more fully described the genusf than any other 

 author, and given all the European species with great care, but has, 

 in my opinion, included in it some forms with quadragonal whorls 

 and siphuncles in different positions which should be separated as 

 Remele has done under the name of Facilituites. 



Estonioceras has a nepionic stage with a large umbilical perfora- 

 tion like that of other species of the same phylum. The apex 

 itself, the ananepionic substage, is remarkably large and grows with 

 extreme rapidity in its transverse diameters, showing the tendency 

 to form a broad, digonal whorl, and is cap-shaped when seen from 

 the side as in Trocholites and Ophidioceras and very large in all its 

 diameters. The sutures of the meta- and paranepionic substages 

 throughout the greater part of the first whorl, as seen in the speci- 

 men Fig. 13, PL vii, and in Schroder's figure of apex of Estonioceras 

 imperfectum, PI. iv, Fig. 5, a-b, reproduced here on PI. vii, Figs. 20 



* Op. cit, Jahrb. d. konig.-preus. geol. Landesan. u. Bergak., 1882. 

 f "Ueber Sil. Ceph.," Pal. Abh., Dames et Kayser, v, lift. 4. 



