1870.| . HANCOCK AND HOWSE—DORYPTERUS HOFFMANNI. 630 
to be developed in connexion with the posterior pair of ventral plates ; 
nevertheless they are probably internal bones. 
On the whole, then, it seems pretty clear that these peculiar 
plates and rods in Dorypterus are the component parts of both an 
endo- and an exo-skeleton. The lozenge-shaped plates or areas are 
the vertebral centres, or rather the remains of them; the lateral 
plates are the neural and hemal spines, and the rods in connexion 
with them are the supplementary spinous processes ; while the hour- 
glass-shaped plates are the interspinal processes or fin-supports, and 
the greater portion of the compound thoracic columns are apparently 
ribs. All these, as well as the great abdominal rods, are component 
parts of the internal bony skeleton. 
The sigmoidal and ventral or thoracic plates, together with the 
upward prolongation of the latter, forming the basal portion of the 
compound thoracic columns, seem to be developments of the skin, 
and consequently belong to an exo-skeleton. The plates, too, that 
apparently correspond on the shoulder to the sigmoidal plates of 
the posterior portion of the body, are most likely also dermal ; and 
if so, the ridges in their transverse centre which form a line extend- 
ing from the nape to some distance down the body are probably true 
mucus-tubes, which they so much resemble. 
There is not much more to say with respect to this matter. We 
may observe, however, that in Doryprerus the ganoid type is modi- 
fied ; and in this interesting form we see, for the first time in the 
geological series, a true thoracic, or rather a true jugular fish of the 
Linnean classification ; for the ventral fins are considerably in ad- 
vance of the pectorals, and, indeed, they are placed as far forward 
as 1t 1s possible for them to be. Some change in the body-scales 
might therefore be expected, though the fins have the usual struc- 
ture of those of the group to which this fish belongs; and the tail 
is decidedly heterocercal, with the lobes, which are deeply forked, of 
nearly equal length. And in the upper lobe there is a double row 
of the usual rhomboidal scales, resembling in their form and mode of 
articulation those on the tail of Acipenser Sturio, Linn. No other 
scales are observed on any part of the body of either of the four 
specimens, unless, indeed, the ventral and sigmoidal plates be so con- 
sidered. We have, then, in Dorypterus a ganoid fish not only de- 
prived of body-scales, but without plates of any kind except those 
just alluded to. 
Having now given the result of a careful examination of all the 
four specimens at our disposal, collating and rigorously estimating 
the facts exhibited by each, we shall now give separate descriptions 
of the specimens themselves, marking emphatically the points for 
which each is distinguished. 
The first specimen (Pl. XLII. fig. 1) that we shall notice is from 
the cabinet of our friend Edward Wood, Esq., Richmond, Yorkshire. 
It is 4 inches long, including the tail, and is about 12 inch deep at 
the deepest part. The anterior portion is well preserved. The head 
is one-third of the entire length of the fish, exclusive of the tail- 
lobes, and is one-third higher than long; itis arched in front, being 
