Maryland Geological Survey 573 



Description.— Hhell with convex dorsal and medially concave ventral 

 valves. The latter has a straight hinge-line and narrow cardinal area, 

 narrow acute beak, and broad plane to slightly convex lateral slopes, while 

 the former or dorsal valve is rotund with umbo full and rounded, and 

 witli l)road median elevation. In general outline the valves are trans- 

 versely elliptical, much wider than long. Exterior covered with uni- 

 formly fine striag crossed by occasional rings of growth. On the interior 

 the ventral valve has a short obcordate muscular scar, while in the dorsal 

 valve the scar is quadripartite, also short. Frequently vascular sinuses 

 cover the pallial region. 



' Schizoijkoriu, striafiilu is a jnendjcr of a chain of closely allied shells 

 occurring at various horizons in the JJevonian, beginning with *S'. prupin- 

 qua Hall of the Onondaga limestone, followed by (J. tulliensis Vanuxem 

 of the Tully limestone; then by S. siriatula Schlotli. of the Ithaca and 

 Chemung. In the upper Devonian of Iowa the same type is represented by 

 S. iowensis Hall wdiich approaches closely to S. tulliensis. 



Schizophoria striatula is a large and robust species attaining uniformly 

 greater size than any of the rest. Its surface markings are also coarser 

 than in its allies; JS. tuUiensis and its western ally S. iowensis are of 

 smaller build with very gibbous dorsal valve, narrow median dcjn'cssion 

 on ventral valve and more sharply sinuous anterior margin: >'. [.rupin- 

 qua is a still smaller less convex and somewhat more graceful shell. 



The genus Schizophora differs from the genus Dalmnneila wliicli has 

 fasciculate stria?, carinate ventral valve and different muscular scars. It 

 differs from Uhipiduniella which has large flabelliform muscular scars 

 in the ventral valve. It differs from both these genera in having convex 

 dorsal valve and sinus in ventral valve. This is one of the most con- 

 spicuous species of the Ithaca fauna, in which it often attains very large 

 size. It occurs more rarely in the I'arkhead and Cheiuung. The indi- 

 viduals from higher horizons are frequently smaller than those occurring 

 in the Ithaca fauna. 



Ltngth large individual 30 mm.; witlth 40 mm. 



Occurrence. — Jennings Formation, Chemung Member. EUerslie, 

 Pennsylvania, 1474 common ; Williams Eoad on Polish [Mountain, 19U7 ; 



