1870.] On Discoid and Turbinated Shells. 529 



Table XI. — To show the relation of temperature of the body to that of 

 the air in the shade, especially in the tropics. 





Temperate Zone. 







Tropics. 









Temperature of air 



Temperature of air 







between 









between 









57°&60°. 



60°&65°. 



65°&70°. 



70°&75°. 



75°&80°. 80°&84° 



Highest 



o 



98 



o 



99 



99£ 



100 



100 



100 





98 



98 



98 



98 



98 



98 



Range 



0 



1 



1* 



2 



2 





2 





98 



98-3 



98-6 



98-63 



98-8 



99-08 







983 







98-836 











Totals. 







Totals. 



Number of markings f98° 



7 



6 



9 



22 



20 



18 



6 



44 



of temperature of | 98£° 





1 



1 



2 



4 



37 



3 



44 



body, taken thrice «{ 99° 





2 



6 



8 



18 



32 



6 



56 



a day, viz. at 9a.m., | 99|° 







3 



3 



4 



23 



12 



39 



3 p.m., and 9 p.m. ^ 100° 





... 







2 



1 



4 



7 







Total 





35 





Total 





190 



Unfortunately the statistics were not sufficiently numerous to draw satis- 

 factory deductions as to the effect of humidity on the temperature of the 

 body in mid-ocean in the tropics, where the amount of moisture is usually 

 considerable. This would be interesting, as would others regarding tro- 

 pical terrestrial climates, in some of which the hygrometric range is some- 

 times smaller, though in the majority greater. 



V. "Observations on the Mode of Growth of Discoid and Turbi- 

 nated Shells." By Alexander Macalister, Professor of Zoo- 

 logy, University of Dublin. Communicated by the Rev. S. 

 Haughton, F.R.S. Received May 4, 1870. 



A most interesting paper on the geometrical forms of turbinated and 

 discoid shells was published by the Rev. Canon Moseley in the Philoso- 

 phical Transactions for 1838, p. 351, in which some important points 

 were noticed regarding the geometrical construction of shell-forms. The 

 author of that paper describes discoid shells as generated by the revolution 

 around a central point of the perimeter of a geometrical figure, which 

 latter, although regularly increasing in size, yet remains always geometri- 

 cally similar in form. The producing figure in many Gasteropodous Mol- 

 lusks is represented by the operculum, and in all it may be recognized by 

 making a vertical section in the plane of the radius vector. A turbinated 

 shell is similarly generated, but the generating figure in the production of 

 the helix slips down along the axis instead of revolving in a constant 

 plane. The Rev. Mr. Moseley gives, as illustrations of these points, mea- 

 surements of Nautilus pompiliusy Turbo phasianus, Turbo duplicatus, and 



