NOMENCLATURE OF STAGES OF GROWTH Wl> DECLINE, 13 



functional siphon in these Bhella Gerard Holm 1 first called attention to the 

 interesting character of the young the Biphon in Endoceras, and lias 



shown tliis organ to have been very large even in the young, baving not only 

 il beginning, as in other forms, but in Beveral Bpecies baving a Bwollen 

 or macrosiphonulate form which endured throughout Beveral Bepta. In speci- 

 mens now in the Museum of Comparative Zoology, at least bus Bepta were built 

 - of contraction began t « > appear. In other cases Bgured l>\ Holm 

 the si phonal cecum, though verj lai mpared with that of Orthoceras, \\a< 



attached to the first septum, as in all the shells bo far known from that group, 

 and occupied «>nl \ the 6 ret air-chamber. We Bhould Buggest to those having 

 il- for Btudy, that the >lu-lls baving this last character are very likely not 

 true Endoceratitea, l>ut perhaps the young of Bpecies of the genus Sannionites, 

 which, according t>> the classification followed by the author, i- a genus distinct 

 the Bpecies possess a much Blenderer Biphon. Whatever 

 the fate "t' this suggestion, it is plain that transitional series exist in this group 

 Snnnionites and Cyrtocerina or Piloceras, and that gradations occurred 

 also in Piloceras, which -how that contraction of the siphon began Brat in adults, 

 ati'l then, according to the law of acceleration, was inherited in the nealogic 

 of immediate descendants, and finally became nsepionic in the smaller 

 siphoned - the genera Endoceras and Sannionites This tendency to 



iction in the diameter of the Biphon indicated the beginning of a series of 

 transformations which accompanied a decrease in size of the fleshy Biphon, and 

 correlative transformations, Buch as the decrease in length of the tunnels, and 

 attraction and Btraightening out of the calcareous endocones, bo as to form 

 ills of a tubular Biphon. In other words, as the siphon contracted, the func- 

 tional endosiphon formed by the open and extended tips of the endocones \\a< 

 finally brought into line with the funnels, and together with them formed the 

 taiphon, which i- consequently a degraded modification derived from the 

 funneli ind endocones of the Endoceratidse. The Orthoceratidas and 



nil the remainii • notable exceptions which we shall take up 



and describe in future papers, had a microsiphon. The whole microsiphon formed 

 narrow diameter, reaching from the last septum to the 

 which represented the macrosiphonula. Doubtless the duration 

 ■ill be found to varj somewhat in ancient forms, but the 

 mown, are iii favor of the theory thai the vast majority of 

 til forms had a microsiphon, which was developed comparatively early 

 in the life of the animal. 



The n< i ng groups would be very interesting if 



there •■ them, but we shall have to illustrate this part of 



our work among the Ammonitinsa. The protoconcha of Ammonoidea, including 



■ iked above, globose forms with calcareous 



Shells, and tie- i tin' a|»-\ of the COnch, hut the 



of the junctions was quite distinct from those of Nautiloids, The eon- 

 n between them and the apt slight in the uncoiled young of the 



