MOLLUSCA FROM JUAN FERNANDEZ AND EASTER ISLAND 239 



Neanic shell (fig. 46) with a more pronounced columellar fold and a trace 

 of a parietal lamella. 



Localities: Masatierra, Aug. 1917: Rabanal, about 300 m above sea, I 

 gerontic empty shell (type, fig. 45). — Puerto Ingles, about 400 m, thick forest, 

 2 neanic small shells (fig. 46). 



From T, callosa the present species differs in its wider aperture and stouter 

 shape, in the absence of a columellar callus and the thinness of the columellar 

 fold, as well as in having, in neanic stage, a feeble parietal lamella. The 

 gerontic stage thus is very like the genus Fernandezia, which, however, is 

 destitute of every armature in the aperture, even in young stages. 



General Remarks on Tornatellina. 



T. bilamellata and T. conica have a common character in the persistent 

 armature of the aperture, this being complete in all stages of growth, though 

 subject to some variation especially in the first-named species. In the three 

 other species described here as new, a difference between young (neanic) and 

 old (gerontic) stages is to be observed, inasmuch as there are lamellae on the 

 walls only in young shells; the ephebic or mature stage seems to be like the 

 neanic one in T. plicosa, but in T. callosa it is similar to the gerontic, which 

 retains the columellar fold only. A reduction of the lamellation thus takes place 

 in the last-named species, about the time of breeding, when the lamellae begin 

 to be resorbed. An analogous reduction was stated in Pacificella variabilis, 

 though in that species the columellar fold is the subject of resorption; other 

 genera, too, such as Lamellina and Tornaie Hides, not to speak of certain 

 Pupillidae, such as Lauria and Orcula, share this peculiarity, which, according 

 toPlLSBRY, is an indication of a great geological age. 



Only the last whorl is, however, in all species, furnished with lamellae, 

 none are found, except occasional traces, within the upper whorls. A continuous 

 resorption of the lamellae thus takes place in all species, as growth passes on, 

 and this reduction also befalls, to some extent, the inner partitions which are 

 always thinner than the basal wall of even young shells. 



The resorption process may perhaps be a consequence of the viviparity 

 of the majority of fam. Tornatellinidae. In oviparous genera such as Auriadella 

 and Tornatellaria, there is a greater similarity between adult and juvenile 

 shells as regards lamellation. 



Observations on Anatomy. 



Some specimens of T. bilamellata were examined by studying series of 

 sections and by dissection; also a couple of T. plicosa in a beginning ephebic 

 stage were dissected. 



The external habitus is like that oi Pacificella (see below): a well-developed 

 right mantle lobe, with a long anal furrow is present. The pallial organs are 

 also similar: the kidney is extremely long and narrow, occupying somewhat 

 more than one whorl, and furnished, at its distal end, with a longitudinal fold. 



