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Show 1 9 0 4 . ] OSTEOLOGY OF CLUPEOID FISHES. 4 8 9 lower edge of the foramen, but does not invariably do so. The temporal foramen is reduced to a pin-point depression in Coilia, and is wanting entirely in Chanos. The pre-epiotic fossa, another Clupeoid feature, is a depression at the side of the cranium, bounded by the epiotic, squamosal, and parietal bones. It is wanting in Chanos ; in Coilia it is entirely obliterated, and in Pristigaster and Hyperlophus largely filled up by the prominent squamosal bulla. The pre-epiotic fossa is probably homologous with the " lateral cranial foramen " of the Mormyroid fishes and Notopterus. The supratemporal bone lies over the aperture of the fossa in tlie Clupeoid fishes, but being a reduced bone it serves less obviously as a cover for the fossa than does the supratemporal for the foramen in the Mormyridse. In Notopterus the supratemporal bone is reduced in size quite as much as in the majority of the fishes now under consideration, and more so than in Dussumieria. The pre-epiotic fossa is bounded by the parietal, epiotic, and squamosal, whereas the foramen of Notopterus and the Mormyridse is set a little lower down, and is surrounded by the epiotic, squamosal, and exoccipital, the parietal in these fishes occupying a position nearer the median plane of the head, and being shut off from the foramen by the union of the squamosal with the epiotic. The suggestion is strengthened by the fact that in Dussumieria the bottom of the fossa is unossified and membranous. If in the preparation of the skull the membrane be removed, the fossa appears as a large foramen leading into the cranial cavity. The lateral temporal groove, situated above and behind the postfrontal bone, is not well marked in the Clupeoid fishes, with the exception of Chanos ; in most cases it is broad and shallow, and is barely recognisable as a groove. There is no subtemporal fossa. The opisthotic bone is as a rule present, but small; it is wanting in Engraulis and Coilia. The bullae in the pro-otic and squamosal bones for the lodgment of caeca! diverticula of the swim-bladder are remarkably constant. Both, however, are wanting in Chanos, and the squamosal bulla is not present in Clupea sprattus, although it occurs in the other species of Clupea examined. The auditory fenestra, bounded by the pro-otic, exoccipital, and basioccipital bones, is also a distinctive feature of the Clupeoids, although it occurs also in Hyodon, in which it is bounded by the same three bones. It is wanting in Chanos and Coilia. The orbitosphenoid and basisphenoid bones are variable in size ; both are wanting in Chanos. In Clupea, Hyperlophus, Chatoessus, and Dussumieria the orbitosphenoid meets the prefrontal bones. The eye-muscle canal opens behind in all but Chanos and Coilia, and except in these two genera and Chatoessus the parasphenoid is produced into a pair of posteriorly directed vertical laminae of bone. In Chatoessus the vertical laminae are present at the sides of the posterior opening of the eye-muscle canal, but they are not produced backward into freely projecting wings. |