REPORT OF THE STATE PALEONTOLOGIST I903 335 



of the endosiphocone. It is hence identical in origin with the 

 endosiphocoleon of Proterocameroceras brainerdi. 



From its lateral ends proceed the endosiphofunicles described 

 above, apparently mostly in longitudinal series. Corresponding to 

 the vertical contraction of the siphuncle the section of the endosi- 

 phuncular _canal is broader than high and its lateral ends coalesce 

 into a conchiolinous blade. As the central portion retains its full 

 lumen, the section becomes in this specimen at first very broadly 

 triangular [fig.4] and finally (through fig.5, 6) a low triangle. The 

 apical termination of this gndosiphuncular canal is not shown in the 

 specimen here sectioned because the ventral portion of the 

 siphuncle has been worn away. There is, however, not more 

 than 1 1 mm wanting of the total length of the siphuncle, and it 

 is therefore evident that no endosiphotube with distinctly cir- 

 cular conchiolinous wall passes, as in Proterocamero- 

 ceras brainerdi, through a large apical portion of the 

 siphuncle. The coloring of the calcite within section 4 suggests 

 perhaps [see enl. pi. 12, fig.3] that also here only a lumen with circu- 

 lar section may have remained open within the endosiphocoleon, but 

 the next section (5) fails entirely to show any inclosed tube. 



We have hence no evidence of the formation of an endosiphotube 

 in Piloceras explanator, but do not doubt that where 

 the siphuncle becomes longer and more tubular instead of remaining 

 short and broad as in this species, an endosiphotube may be formed, 

 as indeed it has been found in other species of Piloceras. 



The wings of the endosiphocoleon in Proterocamero- 

 ceras brainerdi, which originate from a deposit of 

 conchiolinous matter on the outside of the endosiphosheath and 

 which there form such a striking feature, have been observed in 

 but one instance, where the apical portion of the siphuncle is 

 extremely broad and flat and the lateral margins of the endosipho- 

 sheath form hence acute angles. They seem for this reason to have 

 been strengthened by conchiolinous deposits. 



Among the eight species of Piloceras which have thus far been 

 described, one, P. newton-winchelli Clarke [1897, p. 767] , 



