114 NE W YORK STATE MUSEUM 



him iii the Genesis of the Arietidae as a very small, shrunken wart- 

 like appendix, the aspect of which was explained by assuming it to 

 have been composed of conchiolin, which also accounts for its almost 

 invariable absence. In 1893 Clarke (title 20, page 112) announced 

 the discovery of a small fragment of an Orthoceras conch from the 

 Devonic of New York that retains a good-sized calcified protoconch. 

 This minute and interesting specimen was found in the same geolo- 

 gical horizon (Styliola-limestone) with protoconchs of Bactrites and 

 distinguished from them by the central position of the siphuncle. 

 The very similar protoconchs and early stages of Bactrites were first 

 described by Clarke in a subsequent paper (title 23, page 37) and 

 more fully in the first part of the Memoir on the Naples Fauna 

 (page 122). Hyatt in his Phylogeny of an Acquired Characteristic 

 assumes regarding the protoconch of that Orthoceras the stand that 

 this " form certainly has the characters of an Orthoceras, but the 

 protoconch is large and like that of the Ammonoidea. The shell 

 may be transitional from Orthoceras to Bactrites, but it is probably 

 not a typical form of Orthoceras." This view which gives the small 

 fragment from the Styliola limestone still greater phylogenetic in- 

 terest, was later (op. cit., page 130) concurred in by Clarke, who 

 considers it " conceivable that such differences as are here indicated 

 by the young [of Orthoceras and Bactrites] may be totally extin- 

 guished in the later growth stages so that the mature form of the 

 species in question may be before us, though present knowledge 

 does not enable us to recognize it." Even if the unique small shell 

 described by Clarke represents but a transitional form, it demon- 

 strates that there must exist true Orthoceras with like large cal- 

 careous initial chambers. Indeed such were found not long after 

 by Pocta. 



In 1902 Pocta (title 50) published a note on the initial chamber of 

 Orthoceras, his observations being based on the sections of diabas 

 tuffa of the band e^ of the Bohemian Upper Siluric. These sections 

 showed clearly the presence of a baglike protoconch in both longi- 

 conic and breviconic orthoceratites, the species of which, however, 

 could not be determined. Pocta obtained the following conclusions : 



1 The genus Orthoceras possessed a calcareous initial chamber. 



2 The form of the same was baglike, somewhat contracted down- 

 ward, but always of greater width than the first air chamber. 



3 This protoconch exists only in juvenile stages, later it is 

 absent, and its traces in mature individuals are extremely rare 

 (Clarke). 



