222 



DEGRADED AND ABNORMAL RADULA 



CHAP. 



o 



^ 



and is very thick and coloured a deep red or orange (Fig. 122) ; 



in the subgenus Amoria it is unicuspid, in shape rather like a 



spear-head with broadened wings ; 

 in Volittolyria it is of a different 

 type, with numerous unequal den- 

 ticulations, something like the 

 laterals of Mitra or Fasciolaria. 

 Of the Mitridae, Cylindromitra 

 has lost the laterals. Among the 

 Buccinidae, Buccinopsis possesses 

 a curiously degraded radula, the 

 central tooth having no cusps, but 

 being reduced to a thin basal 

 plate, wdiile the laterals are also 

 weakened. This degradation from 

 the type is a remarkable feature 

 among radulae, and appears to 

 be characteristic, sometimes of a 

 wdiole family, e.g. the Columbelli- 



A' 



Fig. 123. — Examples of degraded forms 



of radula: A, Cantharus pagodus dae (Fig. 123, B), SOmetimeS of 



Reeve, Panama (nascent end) X 40; ^ sometimes again of a 



A , same radula, central and front . ° . P 



liortion ;B,ColumbeUavariaSov:h., single SpecieS. Thus in CantJia- 



Panama, x50. ^,^^^ ^^ SubgeilUS of BuccinU71l) 



the radula is typical in the great majoi'ity of species, but in 

 C. pagodus Reeve, a large and well-grown si^ecies, it is most 

 remarkably degraded, both in the central and lateral teeth 

 (Fig. 123, A). This circumstance is the more singular since 



Fig. 124. — Three rows of the radula of Sistrum spectrum Reeve, Tonga, x 80. 

 The laterals to the right are not drawn in, 



C. pagodus lives at Panama side by side with C. ringeus and 

 C. insignis^ both of which have perfectly typical radulae. It is 

 probable that the nature of the food has sometliing to do with 

 the phenomenon. Thus Sistrum spectrum Reeve was found to 

 possess a very aberrant radula, not of the common muricoid 



