lOi Mr. J. D. ^lacdouald on the Anatomy of the genus Atlas. 



the account given of it ; but Do Blainvillc did not hesitate to 

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

 allied to Gasterupteron ; and after his cxanii)le, this error has been 

 repeated in the able Monograph of the Bullidie by Mr. Adams, 

 published in the second volume of Sovverby's ' Thesaurus Con- 

 chyliorum/ a work which is yet in progress. The characters 

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

 lobes. 13ody 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 fi-om 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 rej)rcsent different views of a species of Atlas oecnrnng 

 very plentifully off tlie coast of New Caledonia. 



Fig. 1 . Front \ iew, showing the aperture of tlic mouth, the foot-like 

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

 quiesc'jnt state. 



Fig. 2. Posterior view, showing the eye-specks near the ujjper margin of 

 the frontal aspect of the proboscis. 



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

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

 cessive action of the cilia. 



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

 boscis and ciliated band retracted. The dorsal ])Osition of the 

 anus is also distinctly seen. 



Fig. 5. A lateral view. 



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

 last, but occurring in the same localities : n, 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. H, 9 & 10. Different stages in the evcrsion of the ciliated band. 



Fig. 11. Diagrammatic figure of the animal, showing the relative anatomy 

 of its internal organs: a, the wide pharyn.x; h, the liver; c, the 

 intestine; d, the anus; <?, a protrusiie organ connected with the 

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

 mity o/ 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. 1.3. Loop of one of the generative tubes (seen at 1 1 A) highly magnified, 

 show ing a deposit of dark pigment on one side. 



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



Port Curtis, Feb. 1.3, 1855. 



