Geol.-Vol. I.] SMITH— GLYPHIOCERATIDM. Ill 



who figured a larva of Glyfhiocerasdiadenia Goldfuss, con- 

 sisting of the protoconch with two-thirds of the first whorl 

 attached. Branco^ afterward figured the protoconch and 

 two larval stages of G. diadema at diameters of 0.66 mm., 

 and 0.90 mm. respectively. He noted, too, that on this 

 species the ventral lobe became divided at a diameter of six 

 milhmetres, although his figure I, on Plate IV, shows the 

 ventral lobe broadening and preparing for division at diam- 

 eter of 2.25 mm. But the consecutive larval stages were 

 not figured and described, nor were they compared with 

 known genera, although that does not lessen the value of 

 his data. 



Hyatt in his "Genera of Fossil Cephalopods " often com- 

 pares the larv^ of this group of goniatites to their ancestral 

 genera, but as the paper is not accompanied by illustrations 

 and systematic descriptions of stages of growth of the spe- 

 cies cited, it is not easy to follow the correlations. It was 

 therefore desirable that some typical species of Glyfhioceras 

 should be studied in detail from the protoconch upwards, 

 and material suitable for this was found in G. incismn 

 Hyatt, from the Fayetteville shale, Warsaw division of the 

 Lower Carboniferous, at Moorefield, Independence County, 

 Arkansas. 



Glyphioceras incisum Hyatt. 

 Plates XIII-XV. 



Glyphioceras incisum Hyatt, Geol. Surv. Texas, Fourth An. Report, 

 p. 471, PI. XLVII, figs. 44-48. 



The form is globose, broad, low-whorled, with semilu- 

 nular cross-section, and very involute; in the adult the um- 

 bilicus is closed so that the inner whorls are concealed. 

 The abdomen is broadly rounded and slightly flattened, 

 while the umbiHcal shoulders slope steeply inwardly. There 

 are four or five constrictions to a whorl, visible both on the 

 shell and on the cast. These occurred even in the early 

 larval stages, beginning at a diameter of 0.90 mm., and 

 lasting until old age. 



iPalaeontographica, Vol. XXVII. Beitrage z. Entwick. Foss. Ceph., PI. IV, fig. i. 



