Pisces. | DEVONIAN VERTEBRATA. 601 
Distinguished from the P. /atus (Ag.) by the narrowing of the front, and the very small, quadrangular, 
central plate of the lower side. The dorsal central plate is (as usual in the genus when seen) very large (about 
half the width of the carapace) and hexagonal; granulation resembles that of P./atus ; pectorals very small, 
pointed, scarcely reaching the bottom of the little ventral central plate; tail large and thick. 
Position and Locality—Old Red sandstone, Orkney. 
Genus. COCCOSTEUS (Ag.) 
Gen. Char.—Head and body not distinctly separated ; together forming an ovate carapace, broadly-rounded 
in front, and tapering behind; one nearly transverse suture marks the posterior limit of the nearly semicircular 
head, which is covered by the ‘facial plate” of Agassiz, which latter is divided into three triangular lobes (some- 
times forming separate plates), widest at their outer ends, the middle one having a deep semielliptical fissure 
in the front margin; the space between the middle and lateral lobes of the facial plate on each side is filled by 
nearly equal and similar plates, called the “lateral anterior plates” by Agassiz; the plate called “nuchal 
plate” by Agassiz, is, I think, the homologue of the anterior median dorsal plate of Pamphractus (=back of 
Prerichthys) ; it is a broad, slightly tumid, trapezoidal plate, having two equal oblique sides, one rather wider 
posterior margin, and the anterior margin shorter than the others; the posterior margin is articulated to the 
very large subpentagonal, shield-shaped, dorsal plate, the broad anterior end of which is truncated, the long 
sides subparallel with a slight sigmoidal curve, and abruptly tapering to a sharp point behind; this plate is 
obtusely keeled along the middle, from whence the flattened sides slope. On each side of the nuchal plate is 
the large trigonal “ posterior lateral plate” of Agassiz, the base in front articulating with the cephalic plate, 
the inner margin articulating with the nuchal plate, to the base of which its apex extends; this plate I think 
should be considered the homologue of the anterior latero-dorsal plate of Pterichthys, and he called by the same 
name; behind the apex of the last plate are the much narrower and longer triangular plates, which I have 
called the posterior, latero-dorsal plates, which extend about two-thirds the length of the posterior dorsal 
plate on each side; these are omitted by Professor Agassiz in his restoration, though represented by Miller. 
The jaws are small, curved, and set with several pointed, equal teeth, confluent with the bone of the base, 
and equally destitute of ganoine. Agassiz figures three narrow marginal plates extending from the outer edge 
of the anterior, lateral, cephalic plate, to the outer angle of the nuchal plate, these I have not seen distinctly ; 
between the posterior end of the under jaw, and posterior angles of nuchal plate, covering the cheek on each 
side, is a rather large, triangular, ‘articular plate.” The under side of the body is covered by five plates (the 
plates, if any, beneath the head being unknown), two posterior ventral plates uniting along the middle by 
a broad squamose suture, which shews them when dislocated to be non-symmetrical, the left one being the 
largest and always overlapping the right; they are elongate, oblong, truncated behind, but with the posterior 
lateral angles produced backwards in short falcate spines; the outer sides are nearly straight, the inner angle 
being cut off by the small, acutely rhombic, central, ventral plate, which has broad, squamose bevelling from 
without, so as to underlie the other four plates; the lateral obtuse angles coincide with the transverse suture 
between the anterior and posterior latero-ventral plates ; anterior lateral plates as wide, but only about one-third 
the length of the posterior ones, transversely rhomboidal, the anterior margins nearly straight, and coinciding 
with the apex of the central plate; the outer margin oblique, with the anterior angle rounded, the five together 
forming an elongate, oblong shield. ‘Tail as long as the head and body together; the apophyses of the 
vertebrze strong, bony, but the bodies rarely ossified, usually, as suggested by Agassiz, forming a soft con- 
tinuous cord, as in the recent Lepidosiren, and leaving no trace in the fossil state. There is a dorsal fin 
close to the end of the carapace. Surface of all the plates pustulated, the granules radiatingly striated at 
the base. 
According to Agassiz there is also an anal fin directly under the dorsal one, but after the examination of 
a large number of finely preserved examples belonging to three species of the genus, I have never seen any 
trace of it; in the position indicated I have always observed the apophyses of the vertebrae much longer than 
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