114 THE DEVONIAN OF MISSOURI. 



Valves depressed-convex below, becoming gibbous in the middle and above. In 

 its usual condition of preservation the shell is very much depressed. 



Beaks at about the anterior third, prominent. Umbonal slope sub-angular, denned 

 above, less prominent below. 



Surface marked by fine concentric striae of growth, which are partially preserved 

 in the cast. 



Three specimens measure respectively 33>, 35 and 43 mm. in length, and 25, 29 and 

 30 mm. in height." 



Remarks — -This species is abundant on Cow Creek, near the top of the Snyder 

 Creek shales, but is rare at other places. It exhibits considerable variation. The pos- 

 terior margin varies from obliquely truncate to a nearly regular curve; in some speci- 

 mens the length is one-half greater than the height. In the longer shells the beaks are 

 proportionately nearer the anterior end. All of the specimens are interior moulds and 

 do not retain the surface markings. , The series seem to include forms described by Clarke 

 and Swartz as Schizodus trigonalis. 



Superfamily Mytilacea 



Family Modiolopsidae 



Genus Modiomorpha Hall 



Modiomorpha missouriensis n. sp. 



Plate 25, figures 3-6, 10 and 11 



Description — Shell small; length little greater than the height;, basal margin gently 

 curved; posterior margin rounded in about the same way above and below, narrow at 

 the extremity; cardinal margin oblique; nearly straight though diverging slightly from 

 a straight line at the beaks. Anterior end projecting in front of the beaks, rounded 

 much like the posterior end. Valves moderately and regularly convex. Hinge line 

 extending little more than one-third the length of the shell though its length is about 

 half that of the shell. Beaks small, pointed, directed forward. Umbonal region not 

 sharply set off from the rest of the shell. Test marked by strong, irregularly spaced 

 concentric striae. 



This form differs from M. concentrica (Conrad) in the termination of the hinge 

 line a short d istance in front of t he beaks and the regular downward curve from this point 

 to the anterior end of the shell. The concentric ridges are much coarser than in M. 

 concentrica (Conrad); the shell is comparatively shorter and thicker. 



Occurrence — Snyder Creek shale of Callaway County. 



Genus Goniophora Phillips 



Goniophora hamiltonensis (Hall) 



Plate 25, figures 1 and 2 



1870. Sanguinolites hamiltonensis Hall, Prelim. Notice Lamellibranchiata, 2, p. 36. 



1877. Goniophora hamiltonensis Miller, Cat. Amer. Pal. Fossils, p. 192. 



1885. Goniophora Hamiltonensis Hall, Pal. N. Y., V, pt. 1, Lammellibranchiata 2, 



pp. 296-297, pi. 43, figs. 8-15, 17-21. 

 1901. Goniophora hamiltonensis Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. 



Rept., pp. 684-685, pi. 16, figs. 4 and 5. 

 1903. Goniophora hamiltonensis Clarke, N. Y. State Mus., Bull. 65, p. 390. 

 1909. Goniophora hamiltonensis Grabau and Shimer, North American Index Fossils, 



I, p. 519, fig. 699c. 



