1871.] MR. COLLETT ON THE SKULL OF 6TRIX TENGMALMI. 739 



DESCEIPTION OF PLATE LXXV. 



Fig. 1. Leda tuberculoid, p. 728. 



2. Corbula lirata, p. 729. 



3. striata, p. 728. 



4. Crenclla (Modiolaria) mnltistriata, p. 729. 



5. Nucula crassicostata, p. 729. 



6. Lingula parva, p. 730. 



7. Terebra (Abretia) knockeri, p. 730. 



8. Pleurotoma spiralis, p. 731. 



9. Clathurclla lubiosa, p. 731. 



10. Mangelia angulosa, p. 731. 



11. Nassa pumilio, p. 732. 



12. Ringicula 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 sutcifera, p. 735. 



20. Aclis carinata, p. 734. 



21. Cerithium {Ceriihiopsisl) ca.rina.twm, p. 73(1. 



22. (Cerithiopsisl) gemmuliferum, p. 73(3. 



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. Tomatina TcnocJceri, p. 738. 



5. On tlie Asymmetry of the Skull in Strix tengmahui. 

 By Robert Collett, Member of the Scientific Society 

 of Christiania. (Communicated by Prof. Newton, M.A., 

 F.R.S., V.P.) 



[Keceived June, 1871.] 



In all the StriyidcB 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, 

 Stria' nyctea, S. passerina, S. bubo, S. aluco, and S.jlummea) 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 

 hone, and proceeds downwards by a rather sharp incision in the 

 lateral parts of the ' os occipitale.' In Strix brachyotus and S. otus, 

 on the contrary, this ' crista' appears to be insensibly and without 

 any inflexion joined with the uppermost part of the bone, and con- 



