Pisces. ] DEVONIAN VERTEBRATA. 593 
higher than long, concentrically imbricated ; fins as in the D. brachypygopterus, pectorals long, narrow (gene- 
rally laid against the sides). 
The small fusiform body and very small size and proportion of the scales, which I find constant in four 
specimens now before me, easily distinguish this from the D. macropygopterus and D. brachypygopterus, with 
which M, Agassiz has proposed to unite it. 
Position and Locality.—Old Red sandstone. Not uncommon in the flags of Caithness. 
Genus. CONCHODUS (M°Coy). 
Ref —M°Coy, Ann. Nat. Hist. 2nd Series, Vol. II. 
Gen. Char.—(Teeth in pairs in each jaw as in Ceratodus?); each tooth large, somewhat semicircular, 
pointed in front, subtruncate behind, deeply concave on the grinding surface ; internal margin straight, thickened, 
and with an abruptly deflected edge; external border convex, much raised and strongly undulato-plicate, the 
ridges being largest in front, and gradually diminishing towards the external and posterior portion of the tooth ; 
the plicze are produced by a thickening of the substance of the ridges and a scooping-out of the intervening 
hollows, so that the under side of the tooth remains even; under surface coarsely osseous; upper surface 
polished, with small obscure undulations, and minutely porous. 
This genus is closely allied to Ceratodus and Ctenodus, but differs in the grinding surface being concave; 
the tooth resembling the inside of a plicated oyster. The internal microscopic structure was developed for me 
by the kindness and skilful manipulation of my friend Mr Anthony, of Caius College, Cambridge; it was very 
complex and peculiar, but the prepared fragment has unfortunately been mislaid by him, so that I am unable 
now fully to describe it. I only know one species, the following. 
CoNCHODUS OSTREIFORMIS (M*Coy) Pl. 2. C. fig. 7. 
Ref—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. I. 
Desc.—About one and half inch long, one inch wide, and one line and a half thick; the grinding surface 
deeply concave, the surface of attachment equally convex ; the external semicircular margin gives origin to six or 
seven coarse, rugged, converging ridges, the most anterior about seven lines long, and slightly inclined to the 
straight inner margin, the most posterior is about two lines long, and at right angles with the inner margin ; 
the ridges are separated by deep wide hollows. 
Position and Locality —Found along with Dendrodus latus (Ow.), Holop. giganteus (Ag.), and Hol. 
princeps (M°Coy), in the Old Red conglomerate of Scat Craig. 
Explanation of Figures.—P\, 2. C. fig. 7, palatal tooth, natural size. 
Genus. HOLOPTYCHIUS (4Ay.) restricted. 
Syn. = (Holoptychius Ag.—Rhizodus Ow.) 
Gen. Char.—Body thick, short, rounded; bones of the head granulated ; scales large, very thick, sub- 
rhomboidal, rounded, imbricating, composed of numerous bony layers, exposed surface marked with large, 
longitudinal, flexuous wrinkles and tubercles; teeth small, numerous, conical, longitudinally sulcated at base ; 
tail heterocereal, caudal fin triangular, obliquely truncated; one lengthened, elliptical, dorsal fin, opposite a 
similar anal fin, close to the base of the caudal; ventrals behind the middle of the body. 
I have proposed (Ann. Nat. Hist., July, 1848, page 2) to restrict this genus in the above manner, which 
makes the group much more natural and definite by removing from it those species (principally carboniferous) 
which have very large, thin, quadrate scales, with the minute reticulated structure of Glyptolepis, without the 
longitudinal wrinkles, &c., and haying very large sharp-edged elliptical teeth of two very different sizes In each 
jaw, to which latter I have proposed confining the name Lhizodus (Owen), hitherto considered a mere synonym 
of Holoptychius. 
462 
