Geol.— Vol. I.] SMITH— GLYPHIOCERATID^. I15 



siphonal ccBcum, a pear-shaped knob, projecting a short 

 distance into the embryonic shell. It must have been pres- 

 ent in the embryo, for it is older than the first suture, but 

 its function is unknown. In some specimens what seemed 

 to be a tube could be seen attached to the ccscum; this is 

 probably the prosiphon described by Munier-Chalmas, but 

 no specimens sufficiently definite to figure could be obtained. 

 On PL XIII, figs. I and 2, is shown the protoconch 

 from which all the chambers have been broken off. Dimen- 

 sions : 



mm. 



Diameter o . 46 



Height of whorl at attachment of first chamber 0.24 



Height of first chamber from protoconch o. 17 



Width 0.66 



Involution o. 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 PL XIII, figs. 3, 4, and 5, is shown the protoconch 

 of a Glyphiocei'as from the Carboniferous of Scott County, 

 Arkansas, 2 N., 29 W., section 36, near the center. This 

 species was compared by the writer^ to G. s-phcericum Mar- 

 tin, and said to be identical with the species from Moore- 

 field. But although the adults are nearly alike, the proto- 

 conchs are quite unlike, as may be seen by a comparison 

 of the two figures. The following are the dimensions of 

 the Scott County form : 



mm.. 



Diameter 0.53 



Height of whorl at attachment to the protoconch 0.26 



Height of whorl from the protoconch 0.18 



Width 0.80 



Involution 0.08 



These figures show it to be larger and proportionally 

 broader than the typical G. incisum. If the species are 

 identical then this is an unusual variation. 



1 " Marine Fossils from the Coal Measures of Arkansas," p. n. 



