600 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
granulated, plates of the tail very minutely granular; anal (or dorsal) fin about as high as long, its anterior 
spine rather more than one line thick at base, five lines long; membrane of the fin granular. 
The above description is drawn up from finer specimens than M. Agassiz apparently had access to. 
Position and Locality.— Abundant in the Orkney schists of the Old Red sandstone. 
PTERICHTHYS LATUS (Ag.) 
Ref —Ag. Old Red, t. 3. figs. 3 and 5. 
Dese.—Oblong, carapace about three inches long, width two-thirds its length ; pectorals narrow, gradually 
tapering to a point, curved uniformly with the side of the carapace, the width of which they slightly exceed in 
length ; plates of the tail subquadrate, about one and half lines wide, arranged in transverse (? or alternate) rows. 
Central plate subpentagonal, gibbous, rounded, about equal to the anterior lateral plates in width. 
In all the specimens I have seen the tail-plates seemed to me in alternating rows, and tuberculated more 
finely than the body. What Agassiz has described as the under surface of this species, Sir P. Egerton has 
shewn to be the lateral aspect, so that there is no anomalous absence of central plate. 
Position and Locality—Old Red sandstone, Orkney. 
PTERICHTHYS OBLONGUS (Ag.) 
Ref—Ag. Old Red, t. 3. figs. 1 and 2. 
Dese—Carapace high, narrow, about three and half inches long, oblong, with nearly straight, subparallel, 
plane, perpendicular sides; width (greatest about the middle) one inch nine lines; central plate suboval, 
gibbous, about one-third longer than wide; pectorals about one-fourth longer than the width of the body, 
abruptly pointed ; tail as wide at the base as the extremity of the carapace; head small, rounded, prominent ; 
granulation coarsest at the ends and margin of the carapace. 
Remarkable for its large perpendicular sides and lengthened form. 
Position and Locality —Old Red sandstone, Gamrie, and common at Orkney. 
PTERICHTHYS PRODUCTUS (A¥.) 
Ref—Ag. Old Red, t. 5. 
Dese.—Head and carapace suboval, about three inches long, the greatest width being about half their 
combined length; central ventral plate rather less than the width of the anterior lateral plates, its length and 
width equal, having four slightly curved equal sides and blunt angles; head small, rounded; tail conical, as 
wide at the base as the posterior end of the carapace (that is, nearly half the greatest width), which it about 
equals in length, covered with several longitudinal rows of subquadrate or rounded scales about a line wide ; 
pectorals broad, slightly exceeding the width of the body in length; posterior margin slightly concave ; anterior 
margin nearly parallel with the posterior for two-thirds of its length, then abruptly curving down to meet it at 
a sharp point; granulation coarse, very crowded, 
Position and Locality.—Old Red sandstone, Orkney. 
PTERICHTHYS TESTUDINARIUS (Ag.) 
Ref —Ag. Old Red, t. 4. figs. 1—3. 
Desc.—Carapace about three inches long, ovate, pointed behind, subtruncate but narrowed in front, gibbous 
along the middle; central ventral plate small, longer than wide, with four straight sides and sharp angles, its 
width being little more than half that of the anterior lateral plates. 
