AND MESOZOIC FISHES. 
4.13 
fused condition. The teeth can be seen from all points of view, and a good idea of 
their characters can be obtained. 
The muzzle does not project beyond the lower jaw, so that the nioutli is termi- 
nal. The teeth are confined to the anterior half of the mouth. They are narrow, 
and are arranged end to end in arched rows. The crown is keeled on the middle 
line, a part of the keel not exactly in the center, rising into a low angle. The edge 
is not serrate nor beaded, but is feebly crimped in some teeth, and apparently .smooth 
in others. The surface is otherwise entirely smooth ; but there are on one side 
three low vertical keels. The base of the crown projects over the root on both 
sides, but on one side much more than on the other, so that teeth lying on their 
side, look like short cylinders. Tlie root is coarsely porous, the openings being fre- 
quently as large as the space between them. 
This species resembles in dentition, in some measure, such I'orins as 0. mitins- 
cuhis N. and W.’ and O. elegantulus N. and W.'* The former has. according to its 
describers a distinctly beaded median keel, and in the latter the crown is trans- 
versely ridged; in neither is its swollen base described nor figured. Tlie presence 
of vertical crests on one side of the crown, places the 0. basalis in the section Agas- 
sizodus St. J. and Worthen. In this genus it resembles 0. virginiantis St. .1. and 
W.,‘ and O. scibdus' St. J. and W.; but it is more slender, and has fewer cia'sts 
than the former, and is less slender and moi’e symmetrical than the latter. 
The mandibular ramus becomes shallower jjosteriorly than at the middle. 'I'lie 
scapular arch has the position usual in sharks, and the horizontal anterior ]>()rtion 
rises gradually into the much longer vertical jiortion, which has the anterior Ijorder 
straight. The pectoral fin is too much damaged for interpretation. 
Measuke.wknts. 
MM. 
Length from end of muzzle to superior apex of scapular arch ; 225 
Length of mandible to cotylus ; 11*' 
Depth of mandible at middle ; -- 
Depth of inferior limb of scapular arch ; .21 
Length of a tooth ; *'‘'^ 
Depth of same tooth at apex; 
Depth of crown of same tooth; . 
One half of the slate containing the specimen above described, is contaimal in 
the State Museum at Springfield, Illinois. It was kindly lent me by Dr. .losliua 
Lindahl, State Geologist. Through him I learned that the other half was in posses- 
sion of Mr. Frederick R. Jelliffe, of Galesburg, 111. Mr..Ielliffe very kindly sent me 
his specimen, together with the one already described as Symmomim renijorvie ; and 
I here express my appreciation of his kindness in so doing. 
' Report of the Geological Survey of Illinois, II, 67 ; PI. IV, Fig. 11. 
2 Report of the Geological Survey of Ohio, II, 67 ; PI. VI, Fig. 6. 
» L. c. VI, PI. VI, Fig. 16. 
< L.c. VI, PI. VIII, Fig. 
