PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 363 
similis tending to have prominent differentiation of the primary and postprimary 
elements, whereas in G. bellatula the costellae are less strongly differentiated. 
GLYPTORTHIS BELLARUGOSA (Conrad) 
Plate 48, C, figures 12-18 
Orthis bellarugosa Conrad, Proc. Acad. Nat. Sci. Philadelphia, vol. 1, p. 333, 1843—Hatt, 
Pal. New York, vol. 1, p. 118, pl. 32, fig. 3, 1847.—BaAsster, U. S. Nat. Mus. Bull. 92, 
P. 591, 1915. 
Conrad’s type lot consists of two specimens, one small complete one and a 
larger pedicle valve. The latter preserves the interior well, but the external orna- 
mentation is badly worn. In his description Conrad gives the length of the species 
as “less than half an inch.” It is best then to select the smaller specimen as the 
holotype even though the species attains a greater length than half an inch. The 
type specimen may be characterized as follows: 
Outline quadrate, with gently convex lateral margins but nearly straight an- 
terior margin. Cardinal extremities slightly greater than a right angle; anterior 
commissure rectimarginate ; valves nearly equal in depth, the pedicle valve hav- 
ing a slightly greater depth; surface multicostellate with about 57 costellae ap- 
pearing in 3 generations. Median costella of pedicle valve slightly larger than 
surrounding ones and extending directly from beak to margin. Imbricating con- 
centric ornamentation closely spaced, about 6 imbrications in 2 mm., forming 
rounded, short, blunt spines open anteriorly and at their extremity. 
Pedicle valve moderately convex in lateral profile with the greatest convexity 
located slightly anterior to the umbo. Front third slightly flattened ; fold not well 
defined but median costella elevated throughout its length, and at anterior third 
a costella is intercalated on each side to form a median fascicle that serves as a 
fold. Median region somewhat swollen; lateral slopes even and steep. 
Brachial valve with sulcus originating at beak and extending to anterior mar- 
gin, narrow and shallow throughout its length. Sulcus marked by implantation 
of a costella on each side ; additional costellae implanted on inside and outside of 
these 2 slightly posterior to the middle. Tertiary intercalation of costellae occur- 
ring anteriorly and bringing total number in sulcus to 9. Flanks bounding sulcus 
gently swollen; slopes to cardinal extremities gentle and low. 
Measurements in mm.—Lectotype, length 11.0, brachial length 10.0, width 
12.0, hinge width 9.5, thickness 5.7. 
Types.—Lectotype: A.M.N.H. a; paratype: A.M.N.H. (not numbered). 
Horizon and locality (of lectotype).—Decorah formation (Ion member ?) in 
Wisconsin: At Mineral Point, Mineral Point (30’) Quadrangle. 
Discussion.—The type specimen of G. bellarugosa is characterized by its quad- 
rate outline and its fairly fine costellae. No other specimens in the National 
Museum collections are quite like this one. For that reason it is difficult to 
assign the correct part of the Decorah shale from which the species comes. 
Glyptorthis bellarugosa suggests G. costellata from the Bromide formation 
