18/1.] MR. HARPER PEASE ON POLYNESIAN LAND-SHELLS. 465 



Genus Chondrella, Pse. 

 Typus, Cyclostoma parvum, Pse. P. Z. S. 1864, p. 674. 



Testa globoso-conica, tenuiuscula, striata, imperforata, vel vix ri- 

 mata ; apertuva fere circularis ; peristoma simplex, tenue, mar~ 

 ginibus late disjunct is ; columella callo appresso, late dilatato 

 indutu, locum umbilici tegens. 



Animal tentaculis nullis, oculis supra caput imtnersis. 



Operculum testaceum, solidiusculum, pallidum, nitidum, oblongo- 

 ovatum, latere dextro fere recto, utrinque rotundatum ; extus 

 planum, Icevigatum, nucleo obsoleto, marginibus anterioribus et 

 lateralibus angulatis ; subtus vix concavum, margine rotunde cal- 

 loso, quasi costato. 



The above genus is peculiar in all respects, animal, shell, and oper- 

 culum. It should be classed with Helicinidce. It is widely distributed 

 over the islands of Southern Polynesia. Most common at the Hervey 

 group, where Mr. Garrett has had ample opportunity of examining 

 the animal alive. It has positively no tentacles, the eyes being im- 

 mersed on the head in the situation usually occupied by tentacles. 



Cyclostoma mimdissimum, Sow., the generic position of which has 

 been undecided, belongs to this genus. It inhabits Pitcairn Island. 



Genus Palaina, Semp. 



Palaina, Semp. Journ. de Conch. 1S65, p. 291. 



Pupoidea, Pse. Am. Journ. Conch. 1865, p. 289. 



The two genera above are no doubt synonymous. As there appears 

 to be a difference of opinion as regards the relation of this genus 

 to those of the Diplommatinacea, by reason partly of a want of know- 

 ledge of the characters of its operculum, I furnish the description of 

 that of P. scalariformis, Pse., inhabiting the Caroline Islands. 



Operculum membranaceum, circulare, mult ispir ale ; anfr. 4-5, lente 

 accrescentes, suturu lineari ; extus nitidum, medio depresso-con- 

 cavum, anfr. ultimus rotundatus, margine tenui ; subtus vix con- 

 cavum. 



The outer side is regularly concave to the last whorl, which is 

 rounded, so that the operculum when laid down would rest on its 

 margin. 



It requires repeated efforts and careful manipulation to separate 

 an operculum, an eighth of a millimetre in diameter, from the animal. 

 If macerated in water until the animal matter becomes soft, the 

 operculum is liable to fall to pieces ; while it is impossible to separate 

 it from the animal in a dried state. I have been successful in ob- 

 taining the opercula of all the genera inhabiting Polynesia, except- 

 ing Electrina, Gray, of which 1 have seen no specimens. 



Genus Helicina, Lam. 



Under this genus I merely record the following descriptions and 

 synonyms. 



Proc. Zool. Soc— 1871, No. XXX. 



