GONIATITES. 71 



the protoconoh is a smooth, rather elongate, bo})))iii-shaped, oval body, of which the 

 upper part projeets forward in a lap, whore the first chamber was joined to it. The 

 protoconch was not the whole of the embryo chamber, for a part of the spiral tube 

 nuist have furnished a lodging for the eml)ryo; )>ut after the formation of the first 

 air chamber it is no longer possi))le to determine how long the primitive body cham- 

 ber was. The protoconch corresponds to the primitive nautilian shell from which 

 the .imiuonoids descended, but the parall(>lism is not exact, for the initial chamber of 

 the nautiloids is not calcareous, while acceleration of development has pushed back 

 to the embryo the calcareous shell of the ammonoids. 



In the protoconch is seen the beginning of the syphon, or syphonal civcum, a 

 pear-shaped knob, projecting a short distance into the embryonic shell. It must 

 have been present in the embryo, for it is older than the first suture, but its func- 

 tion is unknown. In some specimens what seemed to be a tube could be seen 

 attached to the csecum; this is probably the prosiphon described by Munier-Chalmas, 

 but no specimens sufficiently definite to figure could be obtained. 



On PL XIV, figs. 1 and 2, " is shown the protoconch from which all the chambers 



have been broken ofl:'. 



Dimensions. 



Millimeter. 



Diameter 0. 46 



Height of whorl at attachment of first chamber 24 



Height of first chamber from protoconch .17 



Width 6B 



Involution 07 



The protoconch is constant in size and dimensions, for several specimens were 

 obtained free from the air chambers. Also a number of others were broken back 

 almost to the protoconch, and the dimensions agreed, as nearly as could be determined. 



On PI. XIV, figs. 3, 4, and 5, is shown the protoconch of a Goniatites from the 

 Carboniferous of Scott County, Ark., 2 N., 29 W., sec. 36, near the center. This 

 species was compared hy the writer* to G. sp/uericm Martin, and said to be identical 

 with the species from Moorefield. But although the adults are nearly alike, the 

 protoconchs are quite unlike, as may be seen by a comparison of the two figures. 



Diineiisiotis of the Scott County form. 



Millimeter. 



Diameter 0. 53 



Height of whorl at attachment to the protoconch 26 



Height of whorl from the protoconch IS 



Width SO 



Involution 08 



These figures show it to be larger and proportional^ broader than the typical 

 G. crenistria. If the species are identical, then this is an unusual variation. 



Ananepionic. — As soon as the first air chamber is formed the animal has left 

 the embryonic and begun the larval stage, and then takes rank with the chambered 

 nautiloids. The suture at this stage consists of a verj- broad ventral saddle, with 

 a pair of narrow, lateral lobes. On PI. XIV, fig. 1, is shown this suture; fig. 6 



"The figures here referred to are those of this monograph. 

 ''Proc. Am. Philos. Soc, Vol. XXXV, p.ll. 



