150 TORNATELLINA. 



Section LAMELLINA Pease. 



Lamellina PEASE, Proc. Zool. Soc. London, 1860, p. 439, for 

 L. serrata Pse. Lamellidea PILSBRY, Nautilus xxiii, March, 

 J910, p. 123, type T. peponum Gld. 



Tornatellinas in which there are one to three vertical pala- 

 tal ribs, either smooth or serrate, placed at intervals in the 

 last whorl, in the neanic stage, often wanting in the adult; 

 columella armed with two or three folds or lamellae, at least 

 in the neanic stage. Type L. serrata. 



In this section the palatal ribs are vertical, while in Torna- 

 tellina the plica? or series of teeth are spiral ; but the T. per- 

 plexa group forms a partial transition. 



The shells are small, up to 3.5 mm. long, thin and delicate. 

 They live in the Bonin and Hawaiian Islands, Polynesia and 

 Micronesia, but have not been found in Melanesia or Aus- 

 tralia. 



The section Lamellidea was designed to include Tornatel- 

 linse with simply folded columella and no palatal armature at 

 any stage of growth; but the type-species, T. peponum, proves 

 to pass through a Lamellina stage. Lamellidea therefore be- 

 comes a synonym of Lamellina. 



Lamellina is a group possessing a complicated aperture- 

 armature in various stages of decadence. In all of the species 

 upon which we have information, the teeth and folds reach 

 their acme in the neanic stage, later development being more 

 or less retrogressive or phylogerontic. In T. serrata the adult 

 stage shows but slight diminution in the lamellae and folds. 

 In T. ogasawarana, T. microstoma and T. polygnampta the 

 armature reaches its fullest development early in the neanic 

 stage and in the ephebic or adult stage all characteristic struc- 

 tures of Lamellina are lost, and there is a return to the sim- 

 plicity of Tonml'-lliimps. The n-latious of such forms can 

 only 'be ascertained by examination of series of different ages. 

 On plates 32, 40 and 'Others, such series are figured. 



In T. of/(istnr<ir<ni(i at least, the embryonic stage has a tri- 

 plicate columella. This might be interpreted as a highly ac- 

 celenit.-d embryo, but in view of the general homology of la- 



