184 THE DEVONIAN OF MISSOURI. 



Family Rhipidomellidae 



Genus Rhipidomella Oehlert 



Rhipidomella oblata (Hall) 



Plate 44, figures 32, 33; plate 45, figures 1-8 



Orthts oblata Hall, 1857, 10th Ann. Rept. N. Y. State Cab. Nat. Hist., p. 41, figs. 1-5 

 Orthis oblata Hall, 1859, Pal. N. Y., vol. Ill, p. 162, pi. X, figs. 1-17, 19-22, 1861. 

 Orthis oblata Whitfield, 1882, Geol. Wis., vol. IV, p. 320, pi. 25, figs. 1, 2. 

 Rhipidomella oblata Hall and Clarke, 1892, Pal. N. J., vol. VIII, pt. I, pp. 210, 225, 



pi. Via, figs. 3, 4. 

 Rhipidomella oblata Girty, 1899, U. S. Geol. Surv., 19th Ann. Rept., pt. Ill, p. 562, pi. 



LXX, fig. 3a. 

 Rhipidomella oblata Clarke, 1900, N. Y. State Mus., mem. 3, p. 58, pi. 8, figs. 14, 15. 

 Rhipidomella oblata Weller, 1903, Pal. N. J., vol. Ill, pp. 304, 350, pi. XXXV, figs. 



9-13; pi. XLVI, figs. 5-7. 

 Rhipidomella oblata Shimer, 1905, N. Y. State Mus., Bull. 80, p. 244. 

 Rhipidomella oblata Schuchert, 1913, Md. Geol. Surv., L. Dev., p. 303, pi. LV, figs. 9-16 

 Rhipidomella oblata Dunbar, 1919, Tenn. Geol. Surv., Bull. 21, pi. I, fig. 1. 



Description — "Shell in the young state longitudinally subovate, and varying from 

 circular to transversely oval in its stages of growth, resupinate. Ventral valve convex 

 at the beak, flattened in the middle, and concave towards the front. Dorsal valve very 

 convex in the middle and towards the beak; beaks of the two valves nearly equally 

 elevated; that of the ventral valve pointed; area very small; foramen large. Surface 

 finely striated; striae frequently bifurcating and curving towards the lateral and cardinal 

 margins, concentrically marked by finer striae and stronger lines of growth, which are 

 numerous in the older shells. 



"Internally the ventral valve is marked by a large foliate vascular impression; 

 impressions of the adductor muscles rarely well preserved, except in the casts. Teeth 

 prominent, and, when entire, rounded and thickened at their extremities. Dorsal valve 

 with a prominent cardinal process and divergent brachial lamellae; a central ridge, more 

 or less prominent, extends from beneath the beak to near the base. 



"[Remarks] * The ventral valve is marked by a broad undefined 



depression down the centre, making the entire valve broadly concave from a little below 

 the beak, and producing a sinuous outline in front. The dorsal valve maintains a gener- 

 ally uniform convexity, its greatest height being towards the beak. 



"In young and half-grown shells the length and height are nearly equal, while in 



older specimens the proportions of length and breadth are often as three to four * * 



* * * * * * * —Hall, 1859. 



Remarks — In the case of the observed specimens, either the convexity of the dorsal 

 valve is uninterrupted, or the valve is slightly flattened, medially, from the beak to the 

 anterior margin. 



Rhipidomella discus (Hall) 9 



Plate 45, figures 9-16 



Orthis discus Hall, 1859, Pal. N. Y., vol. Ill, p. 165, pi. Xa, figs. 7-12, 1861. 

 Rhipidomella discus Hall and Clarke, 1892, Pal. N. Y. f vol. VIII, pt. I, pp; 210, 225. 

 Description — "Shell circular; valves moderately and nearly equally convex. Dorsal 

 valve flattened or slightly depressed in the centre near the beak, the depression becoming 

 broader and undefined below the middle of the shell. Ventral valve regularly convex, 

 becoming flattened towards the lateral and basal margins, sometimes a little elevated in 

 the middle. Area narrow; length equal to or greater than half the width of the shell. 



