514 ON THE AUSTRALASIAN GUNDLACHIA. 



size the subcentral nucleus and regular elliptical outline distin- 

 guish young Gundlachia. 



A fidler knowledge of the development and structure of the 

 genus is very desirable. 



The nearest, in phylogenetic array, to Gundlachia are probably 

 the New Zealand Latia and the Tii^Yiva.n\-A.\\ Ancylastrum. Should 

 Button's Latiidoi win acceptance, which seems doubtful, it might 

 include these. 



The distribution of Gundlachia agrees in part with that of the 

 recent marsupials, and the theory of a Mesozoic or older Tertiary 

 migration to or from Australia across the south pole, when a lost 

 land with a mild climate united Tierra del Fuego to Tasmania, 

 would explain its present position. 



EXPLANATION OF PLATE XXIV. 



Figs. 1, 2, and 3. — Ventral, lateral, and dorsal aspects, magnified, of a shell 



of G. petterdi, Johnston ; collected by Mr. Petterd in a small pool 



north of the First Basin, near Launceston, Tasmania. 

 Figs. 4, 5, and 6. — Ventral, lateral, and dorsal aspects, magnified, of a shell 



of G. heddomei, Petterd (type specimen), from a pool in the quarry at 



the old station near Hillgrove, Brown's River Road, Hobart. Tasmania. 



These six sketches are drawn to the same scale to exhibit difference in 



size and outline, from specimens kindly loaned for the purpose by W. 



F. Petterd, Esq. 

 Fig. 7. — Lateral view of an animal of G. petterdi, withdrawn from the shell 



after saturation in alcohol. Enlarged. 

 Fig. 8.— Dorsal view of another example. Enlarged. 

 Fig. 9. — Jaw of G. petterdi, as seen crushed under the cover glass and 



viewed with 1 in. objective. 

 Fig. 10. — portion of the same, viewed with gth in. objective. 

 Fig. 11. — Central portion of two rows from the radula of G. petterdi, much 



magnified. Figs. 7-11 from specimens collected at Henley Beach, near 



Adelaide, by H. B. Pulleine, Esq., and the writer. 

 Figs. 12, 13, 14, and 15. — Illustrate stages in the growth of Gundlachia sp., 



from specimens collected in the River Avon, near Christchurch, N.Z., 



by H. Suter, Esq. 



