818 General Notes. [August, 
THE GENUS PLEURACANTHUS.—In the AMERICAN NaTurAList for 
April, 1884, p. 413, I gave a brief abstract of the characters of 
the skull of Didymodus, and proposed to regard it as the type of 
a new order to be called the Ichthyotomi. I now give a plate of 
the skull of D. compressus and D. platypterus, sp. nov.—E. D. Cope. 
EXPLANATION OF PLATE XXIII. 
(I owe this plate to the American Philosophical Society, who will publish it in 
the forthcoming number of their Proceedings.) 
All the figures two-thirds natural size exoi fig. 5, which is one-half larger than 
nature. 
FIG. ba —Skull from above, right frontal bone displaced and its ain 
roken off. Posterior apex bro rey from right frontal — bone. 
or supraorbital b that of the right side sipia aag e one A 6 
post inata facet for pagan ery d, frontal fiss E 
Fic, sy pe part of skull of another individual, Ta above; a, occipital 
; 4, parietal; c, cornua of frontal bon 
Fic. 3. Elies erior view of fig. 2, displaying peh f brain case; a, frontal or pati 
etal cartilage bone; 4, sphen oid; c, brain cavity; d, frontoparietal fontanelle ; 
e, hyomandibular condyle (? pate Akhi bone 5. 
Fic. 4.—Anterior part of skull, from below, of a third individual, displaying orbits 
and postorbital processes 
Fic. 5.—Tooth of mee compressus Newb., natural size, posterior view. Er 
Fic. Aem My ry gi ia and mandibular arches of a fourth individual, from 
with 4m, hyomandibular. ie 
Fic. 7- L Superior tooth of external row, without apices of two of fen re din 
e palatine Ree sieges specimen represented in fig. 5; one- half larger 
ook ay anterior ae 
Fic, 8.—Tooth of Dima platypternus Cope, nat. size, from above Lae 
Fic. 9.—Tooth of a second specimen of Didymodus platypternus, from 7 
ORIGIN oF Corat Reers.—Professor A. Geikie sums pte 
eee ese amount of evidence which has iconii gra to 
orth, ‘s i 
owth of coral incom 
nection with subsidence of the sea bottom) is by no ae adele 
orals ; the form of the 
the shore of calcareous débris derived from dead pas of six% 
These are so abundant as probably to represent ¥ wa 2 
‘teen tons of carbonate of lime in suspensio vi tl 
one hundred fathoms of every square mile of the o reaching the 
deepest water these appear to be dissolved — thus furnish 
bottom, but wud accumulate on shallow bottoms, an 
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