No. 382.] DINICHTHVID OSTEOLOGY. 767 
specialization of the lobes occurring in the same region among 
other species, such as D. ringuebergi' for example, and also in 
the plate shown in Fig. 6. We may be sure that it had to do 
with the mode of articulation with the dorso-laterals, perhaps 
serving for the reception of a ridge given off from the latter. 
It would naturally be supposed from the figure that the anterior 
margin was entire, but we cannot avoid a suspicion that a 
sharply pointed projection in the median line has been broken 
off, since a similar fragment with associated bones on exhibi- 
tion at Columbia shows such an anterior projection. Trachos- 
teus, too, has the dorso-median cuspidate in front, but the plate 
is reduced in size to a mere caricature. Even the small dorso- 
median shown in Fig. 6, the original of which is preserved in 
the Oberlin College Museum, shows a broken extension in the 
median line anteriorly, which may originally have been pointed 
or triangular. We have reproduced a photograph of this shield, 
kindly furnished by Prof. A. A. Wright, for the sake of com- 
parison with Fig. 5, as there are several points of mutual 
resemblance. In fact, the stamp of Titanichthys is so strongly 
impressed that we must regard the plate either as belonging to 
an embryonic individual of this genus, or else as representing 
a pygmy species essentially similar to the Titans. It has a 
strong anterior emargination, slender antero-external angles, 
and a relatively large posterior expansion of the dorsal surface, 
all ‘of which characters are possessed in common with Tita- 
nichthys rather than with Dinichthys. Moreover, the antero- 
lateral margins are deeply lobed, and without question these 
sinuses are of corresponding nature with the incisions already 
noted in the dorso-median of T. clarkii. It will be understood 
that the carinal process has been broken away from both speci- 
mens, its point of attachment being just underneath the 
conspicuous posterior expansion of the shield. 
Having now identified Newberry’s “hyoid (?) or ventral 
plate” of T. clarkii as the dorso-median properly belonging to 
that species, the question arises, where is the shield to be 
placed which this author referred to T. clarkii? We can only 
answer, without having seen the specimen, that there is a strong 
1 Amer. Journ. Sci. [3], vol. xxvii (1884), p. 477, Fig. 1. 
