THE NAUTILUS. 



Vol.. XXIV. DECEMBER, 191O. No. 8 



THE METHOD OF PROGRESSION OF SOME LAND OPERCULATES FROM 



JAMAICA. 



BY AMOS P. HKOWN, PII. D. 



Certain operculate land snails from Jamaica, especially members 

 of the genera Annularia, Cohbostylus^ Tudora, Aduinsiel/a and their 

 allies in (lie Ericiida;, move very ra])idly as compared to other land 

 snails of similar size. They are not only rapid in their movements, 

 but erratic; they change the direction ot movement abruptly. All 

 are very timid, and quick to contract the body \vidiin the shell when 

 disturbed; a shadow thrown on one crawling in the sun is sufficient 

 to cause contraction, and the animal then releases hold of the surface 

 on which it is crawling and drops to the ground. In collecting, it is 

 necessary to avoid startling them by a jar of the surface on which 

 they are progressing, otherwise they instantly fall and are lost in the 

 leat-covered surface of the ground. This character, no doubt, is a 

 protective one from birds and other enemies, as land crabs, mon- 

 goose, etc. 



In crawling, when undisturbed, the motion is rapid; but, as noted, 

 its direction may be changed rapidly. This rapid change of direc- 

 tion is possible on account of the shortness of the surface of contact 

 of the foot and also on account of the fact that the actual surface of 

 contact does not involve the whole foot at any time. Observations 

 made upon Adamsiclla variabilis (C. B. Ad.), A. iynihtbris (C. l'>. 

 Ad.), A. irrorata Gloyne, Colobostylus jayanus (C. B. Ad.), C. jy- 

 anus rufilabris (C. B. Ad.), C. banksianus (Sow.), C. bronnii (C. B. 

 Ad.), Tudora armata (C. B. Ad.), Annulariajiinbriatala (Sow.) and 

 Stoastoma pisum (C. B. Ad.) show that all the above land operculatea 



