XI] 



OF VARIOUS UNIVALVES 



557 



Ratio of breadth of consecutive whorU 



Pointed Turbinates 



Telescopium fiiscnm ... 1-14 



Acus siibulatus ... ... 1-16 



*Turritella terebellata ... 1-18 



*Ttirritella imbricata ... 1'20 



Cerithium palustre ... 1-22 



Turritella duplicata ... 1-23 



Melanopsis terebralis ... 1-23 



Cerithium nodulosum ... 1-24 



* Turritella carinata ... 1-25 



Acus crenulatus ... ... 1-25 



Terebra maculata (Fig. 285) 1-25 



*Cerithium lignitarum ... 1-26 



Acus dimidiatus ... ... 1-28 



Cerithium sulcatum ... 1-32 



Fustis longissimus ... 1-34 



* Pleurotomaria conoidea ... 1'34 



Trochus niloticus (Fig. 286) 1-41 



Mitra episcopalis ... ... 1-43 



Fusus antiquus ... ... 1*50 



Scalaria pretiosa ... ... 1*56 



Fusus colosseus ... ... 1-71 



Phasianella bulloides ... 1-80 



Helicostyla polychroa ... 2-00 



Those marked * from Naumann; the rest from Macalisterf. 



In the case of turbinate shells, we require to take into account 



the angle 9, in order to determine the spiral angle a from the 



ratio of the breadths of consecutive whorls ; for the short table 

 given on p. 534 is only applicable to discoid shells, in which 

 the angle 6 is an. angle of 90°. Our formula, as mentioned on 

 p. 518 now becomes 



Obtuse Turbinates and Discoids 



Conus virgo ... ... 1-25 



Conus litteratv.s 1-40 



Conus betulina ... ... 1-43 



* Helix nemoralis ... ... 1-50 



*8olarium pers2jectivtnii ... 1-50 



Solarium trochlea re ... 1-62 



Solarium, magnificum ... l-To 



*Natica aperta ... ... 2-00 



Euomphalus jientangidatus 2-00 



Planorbis corneus ... 2-00 



Solaropsis pellis-serjientis 2-00 



Dolium zonatum ... ... 2-10 



*Natica glaucina ... ... 3-00 



Nautilus pompilius ... 3-00 



Haliotis excavatus ... 4-20 



Haliotis parvus ... ... 6-00 



Delphinula atrata ... 6-00 



Haliotis rugoso-plicata ... 9-30 



Haliotis viridis ... ... 10-00 



R = 



In sin 6 cot a 



For this formula I have worked out the following table. 



t Macalister, Alex., Observations on the Mode of Growth of Discoid and 

 Turbinated Shells, P. R, S. xviii, pp. 529-532, 1870. 



