lOA IMr. J. D. Macdonald on the Anatomy of the ijenus xVtlas. 



the account given of it ; but De Blainville did not hesitate to 

 place it under the head of Akera, conceiving that it was closely 

 allied to Gasteropteron ; and after his example, this error has been 

 repeated in the able Monograph of the BuUida) by Mr. Adams, 

 published in the second volume of Sowerby^s ' Thesaurus Con- 

 chyliorum,^ a work which is yet in progress. The characters 

 there given are as follow : — " Head with two small tentacular 

 lobes. Body divided into two parts by a narrow pedicle. Foot 

 dilated circularly and ciliated at the margin. Shell none.^' Now 

 all these points may be reconciled with the actual state of the 

 case by reference to the accompanying figures; but from what 

 has been stated above, I think I may hazard the assertion that 

 Atlas has nothing whatever to do with the Gasteropoda. 



EXPLANATION OF PLATE IV. 



Figs. 1-5 represent different views of a species of Atlas occurring 

 very plentifully off the coast of New Caledonia. 



Fig. 1 . Front view, showing the aperture of the mouth, the foot-like 

 anterior lip, the bilobed posterior lip, and the ciliated fold in a 

 quiescent state. 



tig. 2. Posterior view, showing the eye-specks near the upper margin of 

 the frontal aspect of the proboscis. 



Fig. 3. A foreshortened view, with the ciliated circle in active motion : the 

 arrows show the path of the undulations produced by the suc- 

 cessive action of the ciha. 



Fig. 4. A back view of the animal creeping on its labial disk, with the pro- 

 boscis and ciliated band retracted. The dorsal position of the 

 anus is also distinctly seen. 



Fig. 5. A lateral view. 



Fig. 6. A species of Atlas of a brilliant green colour, not so plentiful as the 

 last, but occurring in the same localities : a, the constricted an- 

 terior extremity, the proboscis and ciliated band being retracted 

 to the anus, b ; c, the generative openings. 



Fig. 7' Natural size. 



Figs. 8, 9 & 10. Different stages in the eversion of the ciliated band. 



Fig. 1 1 . Diagrammatic figure of the animal, showing the relative anatomy 

 of its internal organs : a, the wide pharynx ; b, the liver ; c, the 

 intestine ; d, the anus ; e, a protrusile organ connected with the 

 intestiniform tube/, noticed in the text. At the opposite extre- 

 mity of this tube two small glandular-looking sacculi, g, are 

 indicated ; h, the small ducts of the lateral convoluted tubes. 



Fig. 12, Natural size of the animal. 



Fig. 13. Loop of one of the generative tubes (-seen at 1 1 A) highly magnified, 

 showing a deposit of dark pigment on one side. 



Fig. 14. A few of the hepatic lobuli also highly magnified. 



Port Curtis, Feb. 13, 1855. 



