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Show 1871.] MR. COLLETT ON THE SKULL OF STRIX TENGMALMI. 739 DESCEIPTION OF PLATE LXXV. Fig. 1. Leda tuberculata, p. 728. 2. Corbula lirata, p. 729. 3. striata, p. 728. 4. Crenella (Modiolaria) multistriata, p. 729. 5. Nucula crassicostata, p. 729. 6. Lingula parva, p. 730. 7. Terebra (Abretia) knockeri, p. 730. 8. Pleurotoma spiralis, p. 731. 9. Clathurella labiosa, p. 731. 10. Mangelia angulosa, p. 731. 11. Nassa pumilio, p. 732. 12. Bingicula suturalis, p. 733. 13. Natica rubro-maculata, p. 733. 14. Scala bairdii, p. 734. 15. miranda, p. 734. 16. Monoptygma (Myonia) puncturata, p. 734. 17. Obeliscus (Syrnola) gracillima, p. 734. 18. Turbonilla costifera, p. 735. 19. Odostomia sulcifera, p. 735. 20. Aclis carinata, p. 734. 21. Cerithium (Cerithiopsis?) carinatum, p. 736. 22. (Cerithiopsis?) gemmuliferum, p. 736. 23. Ethalia lirata, p. 737. 24. plicata, p. 737. 25. Teinostoma solida, p. 737. 26. Cyclostrema tricarinata, p. 737. 27. roseotincta, p. 737. 28. Solariella canaliculata, p. 736. 29. Volvula cylindrica, p. 738. 30. Tornatina knockeri, p. 738. 5. On the Asymmetry of the Skull in Strix tengmalmi. By ROBERT COLLETT, Member of the Scientific Society of Christiania. (Communicated by Prof. N E W T O N , M.A., F.R.S., V.P.) [Eeceived June, 1871.] In all the Strigidee the ' os squamosum ' forms posteriorly a sharp, projecting, and vertical ' crista,' having its greatest width almost exactly behind the 'fossa glenoidalis,' which, with a more or less distinct incision, bends downwards and half forwards in front of the ear-openings, thus serving without doubt to strengthen the organ of hearing in this Family. In the greater number of North-European species (for example, Strix nyctea, S. passerina, S. bubo, S. aluco, and S.fiammea) this ' crista' appears at the top like a round nail, the upper edge of which is separated by a distinct inflexion from the uppermost part of the bone, and proceeds downwards by a rather sharp incision in the lateral parts of the 'os occipitale.' In Strix brachyotusand S. otus, on the contrary, this ' crista' appears to be insensibly and without anv inflexion joined with the uppermost part of the bone, and con- |