0G8 CONTRIBUTIONS TO NORTU AilERICAN ICHTUYOLOGY — IV. 
Order P.-OP[STII()MI. 
( The IS}) ini/ EeJa.) 
Scapular arch suspended to the anterior vertebne. Superior pliaryn- 
j^eals and ])ranchihyals ossified, the third pliaryn^eal a little larger, 
the fourth small. Three basal branchihyals ; inferior idiaryngeals 
distinct; maxillary bone distinct; supraoccipital separating parietals; 
no interclavicles; symplectic present; praicoracoid wanting; i)arietals 
separated by the sui)raoccipital ; air-bladder, if present, without pneu- 
matic duct; dorsal with spines; ventrals, if ])resent, abdominal. The 
fishes of this order differ from other PhysocUsti and agree with the 
Eels in having the scapular arch free from the cranium and attached 
to the anterior vertebne. Two families are known. {o-r.iaQr,^ backward; 
shoulder.) 
ANALYSIS OF FAMILIF.S OF OPISTIIOMI. 
a. Ventral fins wanting; dorsal fin with tlie soft portion well developed. 
MASTACEMllELIDiE, 56 (fc). 
aa. Ventral fins abdominal, of numerous spines and soft rays; soft portion of the dor- 
sal fin obsolete Notacantiii1).e, 56 (c). 
Family LVI (&).— MxVSTACEMBELIDgE. 
[The Spiny Eeh.) 
Bodj' elongate, eel-like, naked or covered with very small scales. 
INIouth oblique, of moderate size, either the snout or the chin being 
produced in a tleshy.appendage ; lower jaw little movable; upper jaw 
not protractile. Teeth small. Gill-openings restricted to the region 
below the convexity of the operculum, the upper part of the oper- 
culum being covered by the skin of the scapular region-; gill-mem- 
branes free from the isthmus ; gills 4, a slit behind the fourth. Pseu- 
dobranchiai small or obsolete. Tail isocercal. Dorsal fin very long, 
the anterior part composed of low, free spines, the posterior of soft 
rays; anal fin with or without spines; caudal fin separate or not. 
Ventral fins wanting; jiectorals small. Air-bladder present. Bran- 
chiostegals 0; pyloric coeca 2 {\\\ MastacemhehiH). Fishes of the fresh 
waters of the East Indies. Genera 2; species about 14. We follow 
Dr. Bean in attaching provisionally to this family a singular fish from 
