PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER Sy 
superimposed over the costae consists of concentric fila only ; the fine radial lines 
often seen in Orthambonites are completely lacking. Nicolella differs from Orth- 
ambonites and most other members of the Orthidae in the possession of promi- 
nent chilidial plates. These are an unusual feature in the Orthidae and their 
strong development in this genus is a very distinctive feature. Internally Nico- 
lella is like Orthis. 
In the United States one species, Nicolella agilera Willard, was placed in this 
genus, but study of the type specimens shows it to be a decorticated example of 
Productorthis. A genuine Nicolella is present in the upper part of the Chambers- 
burg limestone, and specimens have been taken from Pennsylvania and Vir- 
ginia. This species has the typical concavo-convex form and the chilidial plates 
but is more finely costellate than usual for the genus. Another species occurs in 
the Trenton limestone at Rochdale, near Poughkeepsie, N. Y. 
NICOLELLA ACTONIAE (Sowerby) 
Plate 39, E, figure 20 
Specimen introduced for comparison with American species. Note chilidial 
plates in brachial valve. 
Figured specimen.—t1098838. 
Horizon and locality—Lyckholm formation (F Ia): Moe near Taps, Estonia. 
NICOLELLA ANGULATA Cooper, new species 
Plate 42, H, figures 45-47 
Shell large for the genus, concavo-convex; wider than long; hinge forming 
the widest part of the shell; sides gently curved; anterior margin broadly 
rounded ; anterior commissure broadly sulcate ; surface marked by strong angular 
costae, 16 to 22, with bifurcations near the margins in large specimens. 
Pedicle valve strongly convex in lateral profile and with a strongly rounded 
umbonal region ; anterior profile strongly convex, with steep slopes to the lateral 
margins ; median region inflated. 
Brachial valve moderately concave and with the most concave part in the 
median area; posterolateral areas flattened. 
Measurements in mm.—Holotype, length 10.2, brachial length 9.2, width 12.5, 
hinge width 14.4+, thickness 2.9. 
Types.—Holotype: 116888. 
Horizon and locality——Wappinger formation in New York: On Wappinger 
Creek at Rochdale, 44 miles east-northeast of Poughkeepsie, Poughkeepsie (15’) 
Quadrangle. 
Discussion.—This species is quite unlike O. strasburgensis because of its 
strongly angular, unusually strong costae. 
