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It is questionable, however, even in this form, whether there was 

 anything more than a flattened dorsal side on the septate part of 

 the whorl, since this is the aspect of the perfect side, the left side of 

 this specimen, the right dorsal side and part of centre being crushed 

 in by pressure. A second specimen of smaller size shows the pecu- 

 liar dorsal aspect of Cranoceras depressum, but so faintly that the 

 gibbous face and flutings are hardly perceptible. 



I have been, of course, struck by the resemblance of these shells 

 to the young of the nautilian forms of the Mesozoic, but there is 

 still closer resemblance in the general aspect of species of Urano- 

 ceras and the closely set septa of the species of Cranoceras, and 

 their contracted apertures show that it is not safe to consider them 

 as radical forms. 



They resemble the young of some species of the Nephritidae, but 

 this family has a peculiar ornamentation in young shells and is a 

 closed generic series having apparently its own slender radical 

 forms in the Devonian and possibly even its own arcuate radicals 

 in this period. 



Nephritidce. 



This family name is given to cover a series of genera having 

 heavily ridged shells in the young, and for the most part in adults, 

 with whorls having considerable resemblance in general outline and 

 sutures to the true Nautilidse, with which I formerly associated 

 them. 



Sphyradoceras, described in my Genera of Fossil Cephalopods, 

 page 298, contains the remote radicals of the group and this genus 

 has arcuate and trochoceran forms. They are of value in this con- 

 nection only in so far as they show that the impressed zone, as a 

 rule, is not present when shells are not in close contact. 



Uranoceras has a number of large stout shells with solid, nautilian- 

 looking whorls which are, however, never, so far as I have seen, in 

 sufficiently close contact to produce a contact furrow. These forms 

 are interesting, however, because the dorsum is always slightly 

 flattened and has the aspect common to the nepionic stage of 

 nautilian shells, so that one continually expects to find a specimen 

 with a dorsal furrow. I have, however, not yet found an example 

 of this kind, although the whorls are often so close as to touch 

 each other. The type is Uranoceras (Cyrf.?) uranum, sp. Barrande, 

 in the Silurian, but most of the species occur in the Devonian. 



