70 DR. LEIDY.— MISCELLANIA ZOOLOGICA. 



podal disk. In Bulimus fasciatus it extends backwards as far as the tail, is one-eighth 

 of an inch in width, and is twice folded upon itself ; in Glandina truncata it extends 

 the length of the podal disk ; in a number of American species of Helix, I found it to 

 vary from a superficial depression to a sac the length of the podal disk ; in a specimen 

 of Helix pomatia of Europe, hardened in alcohol, it proved to be a funnel-shape exca- 

 vation half an inch deep ; in Succinea oUiqua it is of moderate length ; in Limax 

 and Arion it is a superficial depression ; and in an undescribed species of Vaginula, 

 a sac half an inch in length and free. 



It is composed of two laminae ; a delicate lining mucous membrane and an external 

 layer, having a whitish or reddish glandular appearance. A large nerve, on each 

 side, from the suboesophageal ganglia, is distributed to its commencement, besides 

 which it receives numerous smaller branches along its course, from the same ganglia. 

 Its arterial supply is derived from the cephalic branch of the aorta. 



This organ, from its situation, relative size to the degree of perfection of the 

 olfactive sense, its structure, and nervous supply, I think, is the olfactory organ. 



