GLYPHIOCERATI'DAE Hyatt 

 Gastrioceras Hyati 



The genus Gastrioceras was established by Hyatt^ for evolute 

 forms with a wide umbilicus, ribs or tubercles on the flanks, trape- 

 zoidal or semilunar cross-section with a high median saddle of the 

 siphonal lobe, two lateral lobes, and two saddles. Later on Karpinsky^ 

 published his beautiful studies about the limitation of the genus, show- 

 ing that there is not really a great difference between it and Glyph- 

 ioceras if the extreme forms are taken into account. According to 

 Karpinsky, the suture is entirely identical and the principal differences 

 should be found in the trapezoidal cross-section, the presence of ribs 

 or tubercles on the flanks, and a wide umbilicus, in Gastrioceras. With 

 respect to the cross-section, we shall show how different this is in the 

 different stages of age of the same species. 



With respect to the ornamentation, J. P. Smith^ has shown that 

 some species of Gastrioceras lack those ribs altogether, as G. glob- 

 ulosum Meek and Worthen, "while some species of Glyphioceras have 

 umbilical ribs, and, in their youth, also the elliptical cross-section, as 

 Glyphioceras diadema Goldfuss." 



Thus there remains only the wide umbilicus to distinguish Gastrio- 

 ceras from Glyphioceras, certainly not a very good character to base 

 the distinction of genera on ; but as it refers only to the very extremes 

 of both groups, the distinction between Glyphioceras and Gastrioceras 

 might be justified. Unfortunately even this character does not hold 

 good when we take Glyphioceras in the sense Haug* and Smith^' regard 

 it, and include, for example, G. calyx Phill., which is an evolute form. 



Karpinsky evidently doubted the validity of the genera Glyphioceras, 

 and Gastrioceras, and has not been able to separate them satisfactorily. 

 Neither have Haug and J. P. Smith; but as it certainly is desirable 

 to divide these forms and as generally only extreme cases are doubtful 



'Hyatt, Gen. of Foss. Ceph., p. 327. 



^Karpinsky, Amm. d. Artinsk-Stufe, p. 45, et. seq. 



"Smith, J. P. Garb. Amm. of America, p. 83. 



*Haug, Bt. s. 1. Goniatites, p. 26. 



'Smith, J. P., Garb, Ainm, of America, p. 63. 



