214 Systematic Paleoxtology — Middle Devoxiax 



MOLLUSCA^ 



Class PELECYPODA 



Order PRIONODESMACEA 



Family SOLEMYACIDAE 



Genus PHTHOMA Hall 



PiiTiiONiA SECTiFRONS (Conrad) 



Plate XXI, Figs. 5-7 



Cypricardites sectifrons Conrad, 1842, Jour. Acad. Nat. Sci., Phila, vol. viii, 



p. 245, pi. xiii, fig. 8. 

 Phthonia sectifrons Hall, 1870, Prelim. Notice Lamellibranchiata, 2, p. 70. 

 Phthonia sectifrons Hall, 1885, Pal. N. Y., vol. v, pt. i, Lamellibranchiata ii, 



p. 475, pi. Ixxviii, figs. 10-13. 

 Phthonia sectifrons Keyes, 1891, Johns Hopkins Univ. Circ, vol. xi, p. 29. 

 Phthonia sectifrons Clarke, 1903, N. Y. State Mus., Bull. 65, p. 489. 



Description. — " Shell above the medium size, elongate, subelliptical, 

 somewhat obovate; length more than twice the height measured at the 

 posterior end; basal margin nearly straight in the middle, curving grad- 

 ually at the anterior and more abruptly at the posterior end; anterior 

 end short, narrowly rounded ; posterior extremity rounded below, oblique 

 and subtruncate above. Valves depressed, convex along the basal and 

 posterior portions, becoming somewhat gibbous in the middle and above; 

 beaks subanterior, small, low and appressed; umbonal slope obtusely 

 subangular in the upper part; above this, and slightly diverging, is 

 another low ridge extending to the middle of the posterior end. Surface 

 marked by fine concentric striae, and by numerous fine radii extending 

 from the beak to all parts of the shell, which are stronger on the umbonal 

 ridge and anterior end than those on the middle of the shell; at the 

 crossing of the radii and concentric striae, the test is raised into minute 

 elongate nodes." Hall, 1885. 



A broken external impression of a left valve of this species was found 

 on the Williams Road near the Church 34 miles southeast of Cumberland. 

 It was compared with the type specimens in the office of the N. Y. 



^ Contributed by Charles S. Prosser with the addition of Onondaga species by 

 E. M. Kindle as indicated. 



