434 
THE PALEONTOLOGY OF MINNESOTA. 
[Orthis (Hebertella?) bellarugosa. 
Orthis (Hebertella?) bellarugosa Conrad. 
PLATE XXXIII, FIGS. 1—4. 
1843. Orthis bellarugosa CoNRAD. Proceedings of the Academy of Natural Sciences of Philadelphia, 
vol. i, p. 333. 
1847. Orthis bellarugosa Hall. Palaeontology of New Yorlc, vol. i, p. 118, pi. xxxn, fig. 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 farrow; 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 pjates 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 
