LEPTOLEPID 
521 
Genus THRISSOPS, Agassiz. 
[Poiss. Foss. vol. ii. pt. i. 1833, p. 12.] 
Head small and teeth minute ; sclerotic ossified. Maxilla arched, 
with a slightly convex dentigerous border; mandible prominent, 
the dentary apparently intermediate in form between that of 
Leptolepis and Aethalion. Opercular apparatus as in Leptolepis. 
Vertebral centra well ossified, strengthened by a median lateral 
ridge; the free neural arches in the abdominal region much elon¬ 
gated and thickened, the ribs also especially robust. Pelvic fins 
much smaller than the pectorals ; dorsal fin small and short-based, 
opposite to the anal fin, which is acuminate in front and ‘much 
extended behind ; caudal fin forked. Scales completely covering 
the trunk ; no enlarged or thickened ridge-scales. 
Thrissops formosus, Agassiz. 
1833-44. Thrissops formosus, L. Agassiz, Poiss. Foss. vol. ii. pt. i. p. 12 ; 
pt. ii. p. 124, pi. lxv. a. 
1844. Thrissops subovcctus, L. Agassiz (ex Miinster, MS.), ibid. pt. ii. 
p. 128 (undefined). [Fish ; Pakeontological Museum, Munich.] 
1839. Thrissops ovatus, G. von Munster, Neues Jakrb. p. 680. [Fish ; 
Palaeontological Museum, Munich.] 
1852. Thrissops formosus, F. A. Quenstedt, Handb. Petrefakt. p. 219, 
pi. xvii. fig. 19. 
1863. Thrissops formosus, A. Wagner, Abb. k. bay. Akad. Wiss., math.- 
phys. Cl. vol. ix. p. 734. 
1863. Thrissops subovatus, A. Wagner, ibid. p. 734. 
1888. Thrissops formosus, K. A. von Zittel, Handb. Palgeont. vol. iii. 
p. 273, figs. 280, 281. 
Type. Nearly complete fish ; Palaeontological Museum, Munich. 
The type species, attaining a length of about 0*5. Head with 
opercular apparatus occupying from one-eighth to one-seventh of 
the total length of the fish; maximum depth of trunk much 
exceeding the length of the head with opercular apparatus, and 
contained about three-and-a-half times in the length of the trunk 
from the pectoral arch to the base of the caudal fin. Vertebrae at 
least 60 in number, about 32 being abdominal and 28 caudal. 
Pelvic fins arising much nearer to the anal than to the pectorals 
and comprising about 5 rays; dorsal fin, with 14 rays, arising 
somewhat behind the origin of the anal, which is much elevated 
in front and comprises not less than 30 rays; caudal fin very deeply 
forked and the lobes slender. Scales partly ornamented with 
delicate radiating striae. 
