500 
ACTINOPTERYGrll. 
15499. Portion of similar but much larger squamation, exhibiting 
the canal of the lateral line penetrating the scales ; Brazil. 
Completely ossified vertebral centra are shown in the 
section. Purchased, 1843. 
P. 7585. Imperfect caudal pedicle and fin, with similar scales; 
Brazil. The fin-rays, 10 or perhaps 12 in number, are 
extremely robust, much divided, expanded, and closely 
divided distally. The largest measures 0*11 in length, 
and the fin seems to have been little if at all excavated 
at the hinder border. History unknown. 
Family LEPTOLEPIDzE. 
Trunk elegantly fusiform. Head with delicate membrane-bones, 
the suborbital and circumorbital plates almost or completely cover¬ 
ing the cheek, more or less enamelled ; parietal bones meeting in 
the middle line ; snout not produced; mandibular suspensorium 
nearly vertical or inclined forwards, but gape of mouth wide ; pre¬ 
maxilla very small; maxilla large, loosely attached and with two 
well-developed supramaxillary plates; teeth small and conical. 
Opercular apparatus complete. Vertebral centra well-ossified, but 
always pierced by the notochord ; ribs delicate ; no fused or ex¬ 
panded haemal arches at the base of the tail. Intermuscular bones 
present. Fin-fulcra absent; fin-rays more or less divided and 
articulated distally ; dorsal and anal fins small, the former usually 
short-based, above or behind the pelvic pair. Scales thin, cycloidal 
and deeply imbricating, usually ganoid in their exposed portion; 
lateral line not observable. 
Synopsis of Genera. 
I. Dorsal fin in advance of anal fin, which is not 
much extended. 
Dentary bone sharply rising into a thickened 
obtuse elevation near its anterior end . . Leptolepis (p. 501). 
Dentary bone gradually deepening from the 
symphysis backwards without any marked 
thickening. Aethalion (p. 518). 
II. Dorsal fin opposed to anal fin, which is much 
extended. 
Dentary bone as in Aethalion 
Thrissops (p. 521). 
