748 STUART WELLER 
face of the disk ornamented with from 18 to 20 radiating cor- 
rugations on each quadrant, which extend about two-thirds of the 
distance from the periphery to the center. Each groove upon the 
corrugated surface extends to the tip of one of the narrow lobes 
of the periphery. Central portion of the disk within the prox- 
imal ends of the corrugations, with the exception of the central 
depression, plane. The whole surface of the disk, in well-pre- 
served specimens, minutely pitted. The four ridges which 
divide the disk into lobes start from four angles upon the cen- 
tral stemlike process. These ridges upon the more weathered 
specimens become nearly or quite obsolete distally. The lobed 
periphery of the disk is rarely perfectly preserved, and in only 
the best-preserved specimens can the minutely pitted surface be 
observed. 
The specimens figured are from the collection of Mr. L. H. 
Hyde; beside these the species is represented in the collections 
of Walker Museum and of the Chicago Academy of Science. It 
is the commonest species of the genus which has been observed, 
and to it may probably be referred the specimen figured by 
Miller from St. Paul, Ind. 
Cryptodiscus hydet n. sp. Figs. 3-4. 
Disk 5 to 8° in diameter, deeply lobed between the quadrants 
giving the entire specimens much the form a of Maltese cross. 
Distal margins of the lobes in no case perfectly preserved. Fun- 
nel-shaped depression in the center 10 to 12™" in diameter on 
the plane of the disk, narrowing to the base of the central] stem- 
like process which is 5 to 6™™ in diameter, rounded over the top, 
and rising from 5 to 7™™, a little above the general plane of the 
disk. Surface of the disk smooth, sometimes with shallow, ill- 
defined radial depressions extending from the center along the 
lateral margins of each lobe to the distal angles. In one speci-- 
men a shallow, ill-defined radiating depression is seen extending 
from near the center of the distal margin towards the proximal 
angle. The four ridges which divide the disk into quadrants, start 
from four angles upon the central stemlike process and are 
prominent to the bottoms of the lobes of the periphery. 
