324 NEW YORK STATE MUSEUM 



the third camera the siphuncle attains its normal dimensions. 

 This subgenus is made to include Nanno aulema, Nanno 

 belemnitiforme and two new smaller forms. It is ap- 

 parent that we would have to enlarge greatly the definition of 

 this subgenus if we wished to commit our form, with its very 

 long but slightly inflated apical cone, to it. 



The question is, however, quite differently viewed by Hyatt. 

 This foremost of the later authors on fossil cephalopods sub- 

 jected the remarkable type from the Minnesota Trenton to an 

 independent investigation and came to a different conception of 

 the genus Nanno [1895, p. i]. It is evident from his discussion 

 of the relations of Nanno to other genera, as also from his reference 

 of Holm's species En doc eras (Nanno) belemniti- 

 forme to Vaginoceras and his later definition of the genus in 

 Zittel-Eastman's handbook [p.515], that he did not see in the 

 large inflated apical cone more than a primitive character of the 

 nepionic stage, which may be retained in various genera, but 

 considered the restriction of the " endosiphuncle " (endosipho- 

 tube) to the apical end as well as the absolute contact of the 

 shell and siphuncular wall on the ventral side, which leads to a 

 bending of the sutures apicall}^ into a lobe passing around the 

 siphuncle, as those characters of Nanno which are of generic 

 importance and differential from the similar genus Narthecoceras. 

 Thus defined, the genus Nanno becomes restricted to the single 

 species Nanno aulema and this is to be regarded as a 

 modified descendant of a genus which retains the endosiphotub^ 

 throughout life. In regard to C a m e r o c e r a s b r a i n e r d i we 

 have shown that the endosiphotube passes not only through the 

 apical cone but also through a large portion of the siphuncle of the 

 shell to a point near the endosiphocone where it enters the endosi- 

 phocoleon. For this reason a reference to the restricted genus Nanno 

 is impossible even if the siphuncle were in as close contact with the 

 conch in our species as in Nanno aulema. 



The septal necks or funnels of the Valcour form reach only 

 from the septum of origination to the next apicad of this [see pl.i, 

 fig.2], ahd the siphuncle is lined by an inner, thick, continuous 

 layer (endosipholining). If we, hence, accept Hyatt's division of the 

 forms originally comprised under Endoceras into the genera Vagino- 

 ceras, Cameroceras and Endoceras by the criterion of the relative 



