OSTEO&LOSSID^.-NOTOPTEEID^. 
85 
Genus THRYPTODUS, Loomis. 
[Palseontogr. vol. xlvi. 1900, p. 229.] 
An imperfectly known genus with depressed skull and small 
mouth, apparently differing from Flethodus in having two lower 
median dental plates opposed to the single upper plate. 
Two species, not represented in the Collection, are recognised as 
follows:— 
Tlrryptodus rotundus, P. B. Loomis, loc. cit. p. 235, pi. xxii. 
figs. 1,2.—Upper Cretaceous (I^iobrara Group); Kansas, 
U.S.A. [Upper and lower dental plates ; Palaeontological 
Museum, Munich.] 
Tliryptodus zittel% P. B. Loomis, loc. cit. p. 234, pi. xxi.—Ibid. 
[The type species. Skull ; Palaeontological Museum, 
Munich.] 
The rostrum of this fish closely resembles a fragment from the 
Chalk of Sussex, in the Brighton Museum, provisionally ascribed to 
an Acipenseroid by A. S. Woodward, Proc. Geol. Assoc, vol. xi. 
(1889), p. 31, pi., i. fig. 6. 
Imperfect remains of a nearly similar fish with free premaxillae 
are described thus :— 
PseudoiJiryptodus intermedins, P. B. Loomis, loc. cit. p. 236, pi. xxii. 
figs. 3-8.—Ibid. [Bemains of head ; Palaeontological 
Museum, Munich.] 
Family NOTOPTERIDtE. 
Supraoccipital bone prominent, but parietals partly meeting in 
the middle line ; squamosal reduced and fused with pterotic; a 
basicranial canal; snout not produced; cheek-plates reduced. 
Mandibular suspensorium vertical or inclined forwards and gape 
moderately wide; premaxilla small and maxilla relatively large, 
both entering the upper border of the mouth. Opercular and 
branchiostegal apparatus much reduced, and no gular plate. Verte¬ 
bral centra well ossified, those of the abdominal region with trans¬ 
verse processes ; ribs nearly encircling the abdominal cavity. Pin- 
fulcra absent; caudal fin very small or absent. Scales thin and 
cycloid, extending over the head and opercular apparatus. 
The surviving members of this family are confined to the fresh- 
waters of the East Indies and West Africa. 
