284 PALEOZOIC PALEONTOLOGY. 
rounded, simple plications, which reach to the beak, about six or eight 
of them being included in the sinus and lingual extension of the 
pedicle valve, with a corresponding number on the fold of the brachial 
valve. ‘Toward the front each plication is marked by a slight median 
groove. 
The dimensions of a nearly perfect specimen are: length, 19 mm.; 
width, 17 mm.; thickness, 18 mm. 
UNCINULUS NUCLEOLATUS (Hall). 
Plate XXIX., Figs. 6-9. 
1859. Rhynchonella nucleolata Hall, Pal. N. Y., vol. ILL, p. 227, 
pl. 31, figs. 1 a-f, 2 a-y. 
Description.—Shell subglobular or subcubical in form, longer than 
wide, the anterior view subquadrangular. Pedicle valve suboval or 
subpentagonal in outline, flattened on the umbo, the lateral and front 
margins bending more or less abruptly to the line of junction of the 
two valves. ‘The median portion of the valve depressed toward the 
front in a shallow sinus, which is produced anteriorly into a lingui- 
form extension at nearly a right angle to the plane of the valve. 
Brachial valve more convex than the pedicle, its lateral margins 
bending abruptly to meet the margin of the opposite valve. The 
mesial fold ill-defined, scarcely distinguishable except close to the 
front margin. Surface of each valve marked by from eighteen to 
twenty-two depressed, rounded, simple plications, grooved near the 
margins of the valves and extending to the beak. From three to five 
plications are included in the mesial sinus of the pedicle valve, with a 
corresponding number on the fold of the brachial valve. 
The dimensions of a perfect specimen are: length, 17 mm.; width, 
13 mm.; thickness, 15 mm. 
Remarks.—This shell resembles U. mutabilis, but is less nearly 
globular and has coarser and fewer plications. 
