<>16 GASTROPODA. | P ulnionutn . 



Remarks. This genus is remarkable, being distinguished from 

 the other genera of the family by the situation of the eyes and the 

 absence of a jaw. 



!. Latia neritoides, Clray. 1850. Plate 24, rig. 24. 



Latia neritoides, Gray, P.Z.S.. 1849 (1850), 108 : J. de Conch., ii, 205, pi. t>, 

 f. 16, 17 ; v, 84, 167, pi. 3, f. 10, pi. 7, f. 1, 2 : Conch- Icon., ix, Navicella, 

 pi. 8, f. 34, 35 ; Latia, f. 1, 2 : Ad. G.R.M., pi. 84, f. 7. Pelex lateratis, 

 Gould, U.S. Expl. Exp., xii, 153, f. 176. Latia Petit iana, Fischer, 

 J. de Concb.. v. 1856, 84, pi. 3, f. 10. L. Gassiesiana, Fischer, t.c., 167, 

 pi. 7, f. 1, 2. L. neritoides, Gray : Hedley and Suter, P.L.S. N.S.W. (2), 

 vii, 624 ; Suter, -1. de Conch., xli, 228 ; T.N.Z.T., xxiii, 93 ; I.e., xxxvii. 

 250. 



Shell semiovate, thin and fragile, almost smooth, brown, semi- 

 transparent. Sculpture consisting of microscopic rather distant 

 radiate striae, and fine dense concentric growth-lines. Colour pale 

 to dark brown ; interior dark brown in the centre, the lamina white. 

 Apex posterior, extending a little beyond the margin, with a spiral 

 nucleus of 1 whorl, visible on the right side ; the apex is generally 

 on the left side, but sometimes near the middle of the posterior margin. 

 Mouth large, oval, the thin sharp margin generally rounded, but the 

 posterior part of it is occasionally straightened and forming more or 

 iess distinct angles with the lateral sides, which themselves may be- 

 come almost straight. Inside polished. The lamella has the left 

 attached end near the middle of the left margin, but the right free 

 end does not extend beyond the posterior third of the length of the 

 .shell. 



Length, 8-5 mm. ; breadth, 6 mm. ; height, 3 mm. 



Animal with ringed filiform tentacles, the eyes at their outer 

 bases (Hutton, T. N.Z.I., xiv, pi. 4, f. U). These animals are highly 

 phosphorescent ; this can easily be seen in the dark by disturbing the 

 animals, or by adding a few drops of alcohol to the water (Suter. 

 T.N.Z.I., xxiii, 93). 



Dentition (Hutton, T.N.Z.I., xiv. 156, pi. 4, f. E).-The formula of 

 the radula is 30 x 27 + 1 + 27. The central tooth is small and bi- 

 cuspid ; laterals increasing in size to the 16th, and then diminishing 

 again, they have first 1, then 2, and near the margin 3 cusps. 



Type in the British Museum. 



Hab. North Island of New Zealand, from Whangaroa to Wel- 

 lington, in lakes, rivers, and creeks, mostly on the under-side of 

 stones. 



Remarks. After examining series of specimens from many localities. 

 1 have come to the conclusion that the species described by Gould and 

 Fischer cannot even be upheld as varieties. Many intermediate forms 

 are found, and the characters on which those species were based are too 

 trivial ; it is simply a question whether the aperture is more rounded, 

 elongate, or squarish, and the vertex lateral or more median. 



