122 



CARBONIFEROUS AMMONOIDS OF AMERICA. 



1S()2. (Toniat'dea ovieni \m-. iKtrallehu A. "Winchell, Am. Jour. Sci., 2d 8eri(\s, Vol. 



XXXIII, p. 364. 

 187i>. Goiiiatifrs oweni var. piAntlUUi, J. Hall, Pal. X. Y.. Vol. V. Pt. II. p. 47H. PI. 



LXXIII, figs. 1 and 2; PI. LXXIV, lig. In. 

 1884-.' Miienxfi'mccraii piiranduiiu A. Hyatt, Proc. Boston Soc. Nat. Hist.. Vol. XXII. 



p. 327. 

 18!»7. Gl yphiocerm paraUeluin. Foord and Crifk, Catal. Foss. Ceph. Brit. Mus., Pt. 



Ill, p. 189, fig. 90. 



Shell discoidal involute, laterally compressed, deeply embracing, con- 

 cealing nearly all of the inner whorls. Abdomen highly arched, sides 

 flattened. Whorl high, helmet-shaped, indented to three-fifths of its height 

 by the inner volution, width four-fifths of its height, which is more tluui 

 one-half of the total diameter. Greatest breadth at a point even with the 

 top of the inner volution. Umbilicus narrow, less than one-fifth of the 

 total diameter; umbilical shoulders abru})t and angular. 



Surface marked by about four backward-curving constrictions. 



Septa similar to those of M. oweni, but closer together. 



This species is most nearly related to M. oiveni, but differs from it in the 

 greater lateral compression, the higher whorls, the naiTower umbilicus, greater 

 involution, and greater approximation of the septa. In the young shell the 

 form is more globose, as the writer has seen on a specimen 10 mm. in 

 diameter, broken out of a large shell. In this small specimen the umbilicus 

 was still narrow, and the sides still somewhat compressed, so that even at 

 this stage it could be distinguished from the young of Muensteroceras oweni. 



This young specimen had the following dimensions as compared with 

 the young of Muensteroceras oweni: 



\ M. parallelum. M. owati. 



Diameter 



Height of last whorl 



Height of last whorj from the preceding 



Width of last whorl 



Involution 



Width of umbilicus 



MillimrAers. 



10 

 5.5 

 .S 



MiUimMers 

 10 



4 

 2 

 8. 2.5 



3.5 



The septa at this young stage are still of the glyphioceran type, and 

 very similar to those of the adult except that they are less approximate, 

 and the ventral lobe is less deeply divided by the siphonal saddle. A 



