No. 382.] DINICHTHYID OSTEOLOGY. 759 
The relations of the dorso-lateral plates have been sufficiently 
treated in former papers, in one of which the writer lamented 
the fact that no plates corresponding to the laterals of Coc- 
costeus have as yet been brought to light. It seems really 
quite remarkable that the plate which students of Dinichthyid 
anatomy have been looking for so long, and has heretofore 
been regarded as missing, should finally turn out to be one we 
are all familiar with, and has simply been masquerading under 
another name these many years. We refer to the “c/avic- 
ular,” so named because it was supposed to have formed part 
of the shoulder girdle. Different writers have made various 
guesses as to its position on the body. Newberry! turned it 
end for end, its bifurcations being supposed by him to have em- 
braced the antero-dorso-lateral. Claypole? considers — “ that 
it was external and ventral can hardly be doubted,” — and also 
confuses rights and lefts. Dean ® pictures it in his frontispiece 
as standing vertically and supporting the mandibles. 
According to our interpretation, the plate in question has 
nothing to do with a shoulder girdle, and there is absolutely 
no evidence that the Dinichthyids possessed paired append- 
ages. The clavicular is in the form of a carpenter’s square, 
roughly speaking ; one arm is bifurcated and extends anteriorly 
and outwardly, the other is single, broad, and flat, and is directed 
nearly at right angles with the longitudinal axis of the body. 
The broad arm is homologous with the anterior lateral of 
Coccosteus, and occupies a corresponding position. The heavy 
ridge on its under side fits into a depression running along the 
front margin of the antero-dorso-lateral, and its flat expansion 
overlies a large area of the latter plate, as shown by charac- 
teristic markings (see Fig. 3). The same arm also extends 
across the interval between cranial and dorsal shields, overrid- 
ing a rounded flange at the base of the external occipital. 
The sensory canal running down to the posterior apex of the 
marginal plate is continued on to the clavicular, being trace- 
able along the margin of the transverse arm as far as the right 
1 Loc. cit. (1889), p. 142. 
2 Rep. Geol. Surv. Ohio, vol. vii (1893), p. 110. 
8 Fishes, Living and Fossil. New York. 1895. 
