ONUSTID.'E. 361 



Syn. Siliquaria, Brug., not Forsk. or Gray. Siliqua- 

 rius, Montf. Agathirses, Montf. 



Ex. T. anguina, Linnccus, pi. 39, fig. 5. Operculum, 

 T. anguina, fig. 5, a, 5, h, 5, c. Shell, T. anguina, fig. 5, d. 



This genus was formerly regarded as an Annelid ; its 

 Molluscous nature was first demonstrated by M. Audouin. 

 The typical species is found in the Mediterranean, im- 

 bedded in the Sponges with silicious spicula. 



Species of Tenagoda. 



anguina, Linn. muricata, Born. 



australis, Quoy and Gaim. poljgona, Blainv. 



lactea, Lam. rosea, Quoy and Gaim. 



laevigata, Lam. squamata, Blainv. 



Fam. ONUSTID.E. 



Lingual dentition — ? Rostrum elongated, subcylin- 

 drical, tapering ; tentacles subulate, with the eyes sessile 

 on their outer bases. Mantle-margin simple in front ; 

 branchial plume single. Foot small, cylindrical, used for 

 jumping, not walking, divided into a front expanded, and 

 a hind tapering portion. 



Operculum large, horny, subannular, right half free, 

 nucleus lateral, dextral ; muscular impression sinistral, 

 semilunar, extending the whole length. 



Shell trochiform ; aperture simple in front. 



When these animals progress, they scramble along like 

 the Strombs, and often extending and fixing the front 

 dilated part of the foot, draw the hind lobe up to it, and 

 then make another step, throwing forwards the shell at 

 every movement; they cannot glide like most other 



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