602 BRITISH PALHOZOIC FOSSILS. [Pisces. 
in other parts of the tail, producing something of the appearance of a fin, but without a second or interapophysary 
set of bones, such as support true fins, and such as we see in nine cases out of ten in the dorsal fin of those same 
specimens. I therefore strongly doubt the existence of an anal fin in this genus. Mr Miller has also figured 
pectoral appendages to the C. cuspidatus (O. R. S. t. 3), of which I have never seen a trace; besides which 
they are figured in a wrong situation for pectoral appendages, and are, I think, more probably some of the 
dislocated marginal plates. The microscopic structure of the plates resembles that of Pterichthys, but the cells 
are smaller and more irregular in shape. The teeth have the middle occupied by a coarse network of irregular, 
tortuous, medullary canals, from which the fine calcigerous tubes radiate, I think I have satisfied myself of the 
existence of a short thick spine on the posterior third of the dorsal plate of all the species. 
CoccosTEUS LATUS (Ag.) 
Ref. and Syn. = C. latus Ag. Brit. Ass. Rep. 1842; Poiss. Foss. Vol. I. p. 32; = C. decipiens Ag. Old Red, 
t. 7 to 10. 
Desc.—Head and carapace clavate; entire length about one foot, width about four inches; nuchal plate 
about one and half inches wide at base, one inch two lines long, and seven lines wide in front ; the facial plate 
prolonged backwards into two triangular processes one-fourth of an inch long, one on each side of the narrow 
front of the nuchal plate; dorsal plate about three inches long and one and three-fourths wide ; anterior third 
of the lateral margin concave, middle third convex, posterior third slightly concave in converging to form the 
posterior point; at about one-fourth the length from the apex is a long ovate gibbosity (supporting a short 
thick spine ?), from whence to the anterior margin runs a small mesial ridge; ventral plates very long, narrow, 
the outer posterior angle produced into a narrow curved process upward of half an inch long; mesial ventral 
plate acute-angled, rhomboidal, one and half inches long and one inch wide in the middle ; all the plates with 
an irrregular, scattered granulation, the interspaces with minute vermicular ridges. 
Position and Locality —Old Red sandstone; very common in the black flags of Orkney. 
CoCUOSTEUS MICROSPONDYLUS (M°Coy). Pl. 2. C. Fig. 4. 
Ref.—MCoy, Ann. Nat. Hist. 2nd Series, Vol. II. 
Desc.—This species resembles the OC. ob/ongus (Ag.) in size and granulation, but has a much shorter dorsal 
plate, and the posterior external angles of the posterior ventral plates are produced into long curved processes 
as in the C. Jatus (Ag.), from which it differs in its strong, regular, close granulation ; it differs besides from 
both species in the plates of the carapace being shorter, and most remarkably in the much smaller size and 
slight ossification of the vertebrze, giving a peculiarly weak and slender appearance to the tail. The bodies of 
the vertebree have all left their separate impressions, so that the vertebral column was certainly not in this case 
a continuous cartilaginous cord, as suggested by M. Agassiz in the case of the C. datus, in which they leave no 
trace. There is evidence of a thick spine, about an inch long, being attached to the tuberosity of the dorsal 
plate. The dorsal plate is two and half inches long and one and a quarter wide, with straight parallel sides, 
not being perceptibly narrower in front than at the lateral angles, in which it differs from the C. pusillus 
(M°Coy), as well as in size. 
Position and Locality—Rare in the black flags of Orkney. 
Explanation of Figures.—P1. 2. C. fig. 4, natural size. On the lower left-hand portion of the dorsal plate 
at upper portion of figure, is seen apparently the remains of a spine attached thereto; the left-hand extremity 
of the figure shews the remains of the vertebral column, shewing the separately ossified bodies of the vertebrie, 
with several neurapophyses, and a few distinct traces of the lower spinous processes or heemapophyses, and 
below them the dermal bones of the dorsal fin in reversed position. 
