The Thickness of Tee-Blocks. — Woodworth. ^71> 
The essential characters of this species are its great Bize, 
its slight curvature and the narrowness of the flange. 
In honor of its discoverer I propose to name it from him 
D-inichthys clarki. It comes from the Cleveland shale near 
Berea, O., and is in the collection of the finder. 
A third species of the genus recently found hy the same col- 
lector is in remarkable contrast to the massive form and pro- 
portion which the earlier discoveries led us to assign to Di- 
nichthys. The best specimen yet known shows not only the 
mandible but several of the bones of the head, some of which 
are recognizable in their crushed condition, but others are at 
present undescribed. Sufficient data, however, are at hand for 
the characterization of the species, as in the other cases, by the 
mandible which is exceedingly slender. A complete specimen 
measures about ten inches in length by an inch in 
breadth (see fig.). It is straight and thin, turned up sharply 
in front as shown in the figure to form the mandibular tooth 
which stands almost at right angles to the axial line of the 
mandible and is bluntly pointed. Behind this is the usual 
space, and then the bone rises into a trenchant blade as in D. 
terrelli, meeting the corresponding sheartooth of the upper 
jaw which, though broken and displaced, is 3 x et distinctly vis- 
ible in the suborbital bone. It therefore belongs to the group 
of which the species quoted above is the type, rather than 
to that represented by the older D. hertzeri. 
The essential characters of the new species here defined 
are the extreme slenderness and straightness of its mandible, 
a feature in which it differs from all others already defined and 
which leads me to confer upon it the name Dinichthys gracilis. 
It comes from the Cleveland shale, near Berea. {)., and was 
found by Dr. Clark, in whose collection it remains. 
AN ATTEMPT TO ESTIMATE THE THICKNESS OF 
THE ICE-BLOCKS WHICH GAVE RISE TO 
LAKELETS AND KETTLE-HOLES. 
By J. B. Woodworth. ( ambridgf. Mass. 
Several writers have ascribed the origin of kettle-holes in 
moraines, kames and sand-plains to the melting out of massi - 
