434 THE PALEONTOLOGY OF MINNESOTA. 



[Orthis (Hebertella?) Ix-lhirugosa. 



ORTHIS (HEBERTELLA?) BELLARUGOSA Conrad. 



PLATE XXXIII, PIGS. 14. 



1843. Orthis bellarugosa CONRAD. Proceedings of the Academy of Natural Sciences of Philadelphia, 



vol. i, p. 333. 



1847. Orthis bellarugosa HALL. Palaeontology of New York, vol. i, p. 118, pi. xxxn, flg. 3. 

 1892. Hebertella bellarugosa HALL. Ibidem, vol. viii, pt. i, p. 222. 



Original description: "Semioval; valves nearly equally convex; lesser valve 

 with a mesial subangular furrow; ribs prominent, linear, with unequal bifurcations; 







disk with numerous concentric, prominent, subsquamose wrinkles; apex of larger 

 valve not much elevated above that of the opposite valve; cardinal area rather wide. 

 Length, less than half an inch. 



"Locality: Mineral Point, Wisconsin, (Trenton limestone)." 



Shell subquadrate in outline; biconvex; anterior margin more or less sharply 

 deflected ventrally. Hinge-line equal to, or a little shorter than, the greatest width 

 of the shell. Cardinal area much the widest in the ventral valve, slightly concave 

 and elevated above that of the dorsal. Delthyrium narrowly triangular in the 

 ventral valve and three times as long as wide. Surface marked by unequal costae, 

 varying in number from thirty to fifty-two, increase taking place by bifurcation 

 on the ventral valve, and by intercalation on the dorsal, crossed by numerous, 

 strongly imbricating, concentric lines of growth. 



Ventral valve strongly and evenly convex, sometimes with a very shallow 

 median sinus, greatest elevation on the umbo, with the beak more or less elevated 

 and slightly incurved. Hinge teeth large, supported by well developed dental 

 plates, which join the lateral elevated outer margin of the more or less obcordate 

 muscular area. This area, in the apical portion, is occupied by the transversely 

 striated pedicle muscle; medially by the expanding adductors, while the diductors 

 are situated on each side of the latter. The short, conspicuous and slightly diverg- 

 ing vascular trunks have their origin at the base of a more or less elevated muscular 

 area and terminate rapidly. Large genital spaces are very faintly indicated on each 

 side of the muscular area. Peripheral margin in the valves marked by prominent 

 radiating striae. 



Dorsal valve convex, with a conspicuous, more or less broad, medial sinus. 

 Cardinal area narrow, erect, slightly concave, divided by the delthyrium, which is 

 as wide as long. Crural plates projecting and having their origin at the base of the 

 walls of the delthyrium, which join the conspicuous, transverse apical thickening; 

 and here the strong and simple cardinal process is centrally situated. Dental sockets 

 deep, situated on the posterior-lateral areas of the crural plates. A stout, but short 



