448 PALEONTOLOGY OF NEW YORK. 



SCHIZODUS TUMIDUS. 



PLATE LXXV, FIGS. 1, S. 



Sdtitodus tumidus. Hall. Prelim. Notice I>ameIlibranchialA, 2, p. 94. 1870. 



CfgUterodm " " Twenty-third Rep. N. Y. State Mus. Nat. Hist. Expl. PI. 14, tig. 19. 1872 



(title page, in error, 1873). 

 C!ytlten)doH (Schizodux) iumidits, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 75, 



figs. 1, 2. 1883. 



Shell of medium size, rhomboid-ovate ; length about one-fourth greater than- 

 the height. Basal margin regularly rounded anteriorly, produced a little in 

 the middle and sub-truncate behind. Posterior margin obliquely truncate. 

 Cardinal line short, straight. Anterior end short and regularly rounded. 



Valves convex below, gibbous in the middle and above. 



Beaks at about the anterior third or fourth, prominent, rising considerably 

 above the hinge-line. Umbonal slope sub-angular, bending downward in 

 the middle and continuing to the posterior extremity, producing a nasute 

 extension. 



Surface characters unknown. 



Muscular impression strongly marked. Pallial line distinct. 



The specimen described is a cast of the interior, having a length of 40 

 mm. and a height of 30 mm. 



This species resembles S. appressa in general form, but the umbonal angle is 

 less sharply defined in the cast, the beaks are larger, and the posterior muscular 

 impression is much stronger and nearer to the beaks. 



Formation and locality. In the limestone of the Upper Helderberg group, near 

 Columbus, Ohio. 



