264 The N.Z. Journal of Science and Technology. [July 
Polymorphism in the Common New Zealand Limpet, Cellana radians 
(Gmelin),* by J. Allan Thomson. 
Some two years ago, when attempting to label a series of shells for the 
reference collection of the Dominion Museum, I found great difficulty in 
naming the common limpets which Suter has included in the Manual of the 
New Zealand Mollusca under the name of Helcioniscus radians , with sub¬ 
species argenteus, decorus, earli, affinis, flavus , olivaceus, and mestayerae. 
Iredalef has since shown that the generic name Cellana has priority 
over Helcioniscus, and that several of the names for subspecies are 
preoccupied—viz., argentea, affinis, and olivacea. For the latter he proposes 
a new name, perana, and unites with it argentea. Helcioniscus mestayerae 
is, he states, not a New Zealand shell. Patella antipodum Smith, which 
Suter considered a distinct species, is a common variant of Cellana 
radians. Iredale therefore recognizes— 
Cellana radians Gmelin (1791). 
,, ,, var. decora Philippi (1848). 
,, ,, ,, earli Reeve (1855). 
,, ,, ,, ? chathamensis Pilsbry (1891). 
,, ,, ,, flava Hutton (1873). 
,, ,, ,, perana Iredale (1915). 
Iredale further remarks, A most delightful field of study here reveals 
itself, as the species and varieties are repeated throughout the Dominion, 
and there must be a recognizable cause for the repetition of distinct forms 
in separate localities. An easily determined form is Cellana radians var. 
flava Hutton. This beautiful shell is common at Napier, and lies upon 
the red sandstone rocks, into which it makes hollows, so that it is difficult 
to detach without cutting the rock away. Upon the black hard rocks 
intermingled dark shells are found, and I believe that this yellow form 
will only be obtained when the soft red rocks are available for its develop¬ 
ment. Perfectly coloured shells are rare, as might be anticipated." 
Cellana decora (Philippi) should be removed from the C. radians group 
and placed in the synonymy of C. strigilis. On being shown a photograph 
of the original figure of C. decora, kindly supplied by Mr. C. Hedley, the 
late Mr. H. Suter at once agreed with me that it was a typical strigilis. 
It seemed to me that certain characters of limpets could be considered 
from a developmental and evolutionary point of view. Moreover, Iredale’s 
suggestion as to the influence of the colour of the rock on the colour of the 
shell .seemed worth following up. I have therefore collected extensive 
series of shells from as many localities as possible, including Kapiti Island, 
Titahi Bay, Wellington, French Pass, Stephen Island, Ship Cove, Queen 
Charlotte Sound, Sumner, Lyttelton, Oama.ru, Waitati, Tairoa. Heads, 
St. Clair, Seaview, and Brighton (near Dunedin). Correspondents have 
also sent me series from Auckland and North Auckland, Hawera, and the 
Bluff. I find, however, that the species flava is common only on the east 
coast of North Canterbury and Marlborough and the east coast of the 
North Island, and I have not had an opportunity of studying a satisfactory 
series. The remarks I have to make are therefore only in the nature of a 
progress report. 
* This paper represents the tentative conclusions I have formed in reference to 
the polymorphism of the common New Zealand limpet, but the research is bv no means 
concluded. In a later paper I hope to present figures illustrating the various points. 
At the Congress these were illustrated by actual specimens, 
f Trans. N.Z. Inst., vol. 47, pp. 430-33, 1915. 
