No. 382.] DINICHTHYID OSTEOLOGY. 765 
vascular canals, tenuity of bone substance along the presum- 
able line of fusion, and nature of the free margin correspond- 
ing to the postero-dorso-lateral on the right-hand side of the 
specimen ; but no distinct evidence of a suture line is to be 
observed. It will be remembered that Macropetalichthys also 
affords an instance of fused dorso-laterals.! On the diagrams 
given herewith all exposed or overlapping margins are shown 
by continuous lines, and underlapping margins by dotted lines ; 
round dots are used where the dorso-median passes under the 
flange of the dorso-laterals, and dashes along the overlapped 
inner margins of the latter plates. 
In the region of articulation with the head shield the dorso- 
laterals are extraordinarily heavy. The thickness even exceeds 
that of the occiput, being between 5 and 6 cm. through. Great 
rigidity, however, was necessary in order to hold the claviculars 
firmly in place. The latter were of huge proportions, but com- 
posed of a relatively thin shell of bone. A large area of the 
dorso-lateral was overlapped by the clavicular, as indicated 
by shading in Fig. 4, and the heavy ridge on the visceral sur- 
face of the latter plate was received into a corresponding deep 
depression along the anterior margin of the dorso-laterals. 
Very excellent examples of the clavicular, belonging probably 
to the next species, are to be seen in the Columbia and Oberlin 
Museums. 
Titanichthys clarkii Newberry. 
The dorso-median shown in Fig. 5 is reduced from one of 
Newberry’s illustrations,? the original of which the writer has 
failed to see, although it is said to be still preserved in the 
Museum of Columbia University. It has not been previously 
recognized as a dorso-median, Newberry having figured it in an 
inverted position and referred it to the “under side of the 
body or head.” The dorsal aspect is here represented, and 
we suspect that the visceral side was embedded in the matrix, 
since otherwise Newberry could not have failed to observe the 
er. Nat., vol. xxxi (1897), p- 497 
tas cit. (1889), Pl. III, Fig. 1, described on p. 135. 
