222 



DEGRADED AND ABNORMAL RADULA 



CHAP. 



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

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



spear-head with broadened wings ; 

 in Volutolyria 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, while the laterals are also 

 weakened. This degradation from 

 the type is a remarkable feature 

 among radulae, and appears to 

 be characteristic, sometimes of a 

 whole family, e.g. the Columbelli- 

 dae (Fig. 123, B), sometimes of 



Reeve, Panama (nascent end) , X 40 ; o-PmiQ cnrnptimPQ n era in nf n 



A', same radula, central and front ^. genUS, SOmetimeS again Ot a 



portion; B,Co^wm&e^^a^;anaSowb., single spccies. Thus in Cantha- 

 Panama,x50. ^.^^ ^^ subgenus of BuccinunC) 



the radula is typical in the great majority of species, but in 

 C. pagodus Reeve, a large and well-grown species, it is most 

 remarkably degraded, both in the central and lateral teeth 

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



Fig. 123. — Examples of degraded forms 

 of radula: A, Cantharus pagodus 



Fig. 124. 



Three rows of the radula of Sistrwn spectrum Reeve, Tonga, x 80. 

 The laterals to the right are not drawn in. 



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

 C. insignis^ both of which have perfectly t3^pical radulae. It is 

 probable that the nature of tlie food has something to do withx 

 the phenomenon. Thus Sistrum spectrum Reeve was found tof 

 possess a very aberrant radula, not of the common muricoid 



