33 
Obs. — This is an interesting genns, most nearly related to Se^nionotus 
and Dapedius, and in some respects intermediate between these two forms. 
The long styliform teeth, and certain obscurely recognizable features in the 
head, are most suggestive of Dapedius ; and the depth of the trunk nearly 
approaches that of some of the species of the last-named genus. The dorsal 
ridge-scales, however, and the j)i‘oportions of the median tins, more resemble 
corresponding features in Semionotus ; though this well-known genus is 
distinguished by its dentition, the absence of ventral ridge-scales, the slight 
vertical elongation of the flank-scales, and the greater development and more 
• forward position of the dorsal tin. 
In the vertical elongation of the flank-scales, Dristisomus may also he 
compared with a Liassic genus, Nothosomus, described by Egerton;* but 
in every other known feature of importance these two generic types arc 
distinct. 
Peistisomus gracilis, sp. nov. 
PI. V, Pig. 1 ; PI. VI, Pig. 1 ; PI. VIII, Pig. 1. 
Ohs. — The typical species, P. (jracills^ is so well represented by 
a single complete trunk, that only two other specimeus need be referred 
to for the determination of the characters of the head, while a third exhil)its 
the dorsal and anal fins in unusual completeness. These fossils may be 
enumerated thus : — 
(а) Type-specimen, shown of the natural size in PI. V, Eig 1. 
(б) Somewhat more slender fish, exhibiting the head, but wanting 
the paired fins. 
(c) An imperfect specimen, showing part of the head and opercular 
apparatus (PI. VI, Eig. 1). 
{d) An imperfect specimen with well-preserved median fins (PI. 
VIII, Eig. 1). 
General Form. — The trunk is gracefully fusiform, the maximum 
depth being contained more than two-and-a-half times in the total length. 
The head is triangular and the snout pointed, and the distance from the 
extremity of the snout to the posterior margin of the operculum is not more 
that one- quarter of the total length. The dorsal and anal fins are almost 
of equal size, with a short base-line and much elevated. 
“ ligs. and Descrip. Brit. Org. Eemaiiis,” Mem. Geol. Survey, Ct. Brit., 1S5S, Dec. ix, No. 0. 
