138 
XAT7TIL0IDEA. 
Endoceras Wahlenbergi. — a, portion of the septate part of the shell (nearly one 
third of it), ytith some of the smooth inner shell-layer remaining, natural 
size (s, siphuncle) ; b, portion of the test of another specimen, natural size ; 
c, part of section from fragment of a large specimen, showing siphuncle (s) 
and sheath {sK), natural size ; d, section and siphuncle of young individual, 
natural size ; e, diagram to show average rate of tapering of the species. 
autliors, undGi the name of “ Orthocercis duplex those whose cha 
racters harmonize sufficiently with the species I have now instituted 
Fig. 14. 
