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Show 1904.] OSTEOLOGY OF THE ELOPID.E AND ALBULID.E. G1 from the pi'o-otic floor of the cranium by the eye-muscle vacuity. The character is one which is very difficult of application ; and it is a matter of individual opinion whether such a form as Clupea is to be regarded as having a simple or double basis cranii, for here the parasphenoid is produced backward into a pair of large lateral wings, the space between which is freely open below ; and again, to attempt to discriminate, as Cope does, between Nolo-pterus and Osteoglossum by the former having a " double basis cranii " and the latter a " simple basis cranii " is futile. Since the terms posterior and lateral temporal grooves (or fossa1, as the case may be) have not always been employed in the same sense in connection with the cranium of Teleostean fishes, it may be well to explain that in this paper the prefix " posterior temporal " is applied to that groove or fossa which lies immediately external to the epiotic bone, and the " lateral temporal " to that depression which lies posterior to, and sometimes also above, the postfrontal bone, just above the anterior part, or the whole, of the articulation between the hyomandibular and the cranium. This, I believe, is the most generally accepted usage of the expressions. The former space is occupied by the trapezius and trunk-muscles (Vetter, Jena. Zeitschr. xii. 1878), the latter by the dilatator operculi and other muscles. The posterior temporal groove is roofed over to form a posterior temporal fossa in Arapaima, Osteoglossum, Albula, Elops, Megalops, and Chanos. In Clupea, Dussumieria, Chatoessus, Chirocentrus, and Eugrau-lis tliere is an aperture-the " temporal foramen "-in the side of the cranium, bounded by the parietal and frontal bones. This in life is occupied by a fatty mass, and in the dried skull leads directly from the posterior temporal groove to the cavum cranii. A short distance behind this is a lateral depression--the " pre-epiotic fossa "-situated immediately in front of the epiotic bone, and bounded by the parietal, squamosal, and epiotic. In Coilia there is a small aperture immediately above the most dorsal part of the upper of the two swim-bladder vesicles, which may possibly correspond with the temporal foramen of Clupea and its allies, but the relations of the parts are rather aberrant. Even in Engraulis the pre-epiotic fossa is largely obliterated by the bulging of the squamosal vesicle. The bottom of the depression is composed of cartilage in Dussumieria and in Clupea harengus, as also in Osmerus, where, too, a shallow pre-epiotic fossa is recognisable. In Hyodon and in Coregonus pollan, on the other hand, there is no fossa, but a similar tract of cartilage is present, bounded by the parietal, squamosal, and epiotic bones. The large aperture-the " lateral cranial foramen "-in the side of the cranium of Notopterus and the Mormyridse is bounded by the squamosal, epiotic, and exoccipital*, and may possibly be * It is not bounded in Notopterus by the postfrontal and squamosal as stated by Boulenger (Poissons du Bassin du Congo, 1901, p. 115, and Ann. Mag. Nat. Hist. 1904, vol. xiii. p. 164), nor in the Mormyrida; by the opisthotic and parietal (Poiss. Bass. Congo, p. 49). ■ " ■ ' |