Pisces.] DEVONIAN VERTEBRATA. 603 
COccCOSTEUS OBLONGUS (Ag.) 
Ref—Ag. Old Red, t. 11. 
Desec.—Size and general shape of the C. /atus, but shorter and less clavate, the facial plate not prolonged 
backwards into little angular processes at the sides of the nuchal plate; the dorsal plate is more gradually 
pointed retrally, and the posterior ventral plates shorter, truncated retrally, and the external posterior angles 
terminating in short, obtuse, mucronate points. The granules are radiated at the base, rather larger, more 
regular and closer than in that species, and the intervening spaces minutely dotted; teeth about a line long, 
close set, smooth, conical, the width of their base equalling their height ; mesial ventral plate large, broad, and 
obtusely ovate. 
Position and Locality—Old Red sandstone ; common at Lethen Bar and at Orkney. 
CoccostEus PusiLLus (M/‘Coy). PI. 2. C. Fig. 5. 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. 
Desc.— Head and carapace orbicular, width about two and half inches, length three inches ; tail about as 
long as the head and carapace, of very numerous small, weak (‘slightly ossified) apophyses ; dorsal fin small, 
weak ; dorsal plate subpentagonal, one inch and five lines long, greatest width (at the lateral angles) eight 
lines, tapering to a sharp point retrally, also narrowing about one-sixth towards the subtruncate anterior 
margin ; all the margins concave, the anterior most so; middle of the plate obtusely keeled, the tuberosity and 
fossa (for lodging the dorsal spine ‘) rather more than one-third the length from the posterior apex ; all the 
plates of the carapace minutely and regularly tuberculated, granules nearly equal, about their own diameter 
apart, fourteen in the space of a quarter of an inch, intervening spaces very minutely granulated ; teeth slender, 
cylindrical, pointed, their own diameter apart, one-third of a line in diameter, nearly a line long. 
The very small size and imperfect development of the vertebral apophyses, together with the small size 
and orbicular form of the cephalothorax, easily distinguish this species. The peculiar proportions of the dorsal 
plate, as well as the distance of its tuberosity and fossa from the apex, and the minuteness and regularity of the 
tuberculation, distinguish it from the young of the other species; besides, I find all the characters constant in 
five nearly perfect specimens which I have examined. 
Position and Locality.—Not uncommon in the black flags of the Old Red sandstone at Orkney. 
Explanation of Figures.—P\. 2. C. fig. 5, natural size of full grown specimen ; the lower part of the figure 
shews two posterior, united, latero-ventral plates, under and immediately above which is seen the extremity of 
the dorsal plate. The remains of the vertebral column seem only to have the spinous processes ossified ; the 
right-hand or anterior end of the figure (which shews the ventral aspect) exposes the two dislocated halves 
of the lower jaw, with their teeth; fig. 5a, single perfect dorsal plate of ditto, from another specimen, 
natural size. 
CoccosTEUS? TRIGONASPIS (M°Coy). Pl. 2. C. Fig. 6. 
Ref.—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. 
Desc.—Mesial yentral plate subtrigonal, slightly convex, thirteen lines long and seven lines wide at the 
lateral angles, which are only two lines behind the rounded or very obtusely-angular anterior end; lateral 
posterior margins straight, converging to form the retral point; four or five irregular rows of tubercles, half a 
line in diameter, and less than their diameter apart, run round the margin, leaving a central, ovate, convex 
space more obscurely tuberculated; each tubercle consists of a hemispherical, smooth centre (frequently per- 
forated in the middle), surrounded by a thickened base, which is radiatingly ridged, intervening space irregularly 
dotted. 
