﻿78 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



their normal size but are incapable of being withdrawn within them- 

 selves, as is the case with many piilmonate gastropods. 



Tlie proboscis is rather large, with a length equal to that of the ex- 

 tended foot. Near the head it is round but becomes larger and flat- 

 tened dorsoventrally toward the anterior end. On the ventral surface 

 of the anterior end two oval labial pads flank the slitlike mouth. The 

 proboscis is swung from side to side in elephantlike fashion when the 

 animal is crawling. 



Body (fig. 33, A) : The external region posterior to the foot and head 

 is sometimes referred to as the body, although it is merely a continua- 

 tion of these. It is supported ventrally by the strong columellar 

 muscle and dorsally bears the esophagus and brood pouch. The man- 

 tle is welded to it on each side. On the right side of the body the small 

 pitlike opening to the brood pouch is sometimes conspicuous. 



Mantle (fig. 33, A, B) : The mantle is probably the most important 

 and specialized organ of the gastropod, for it not only bears the glands 

 that secrete the shell but it also serves as a base to which the ctenidium, 

 osphradium, and several excretory and reproductive outlets are at- 

 tached. Essentially the mantle is a thin, fleshy, cone-shaped cape 

 that hangs over the body. It is appressed closely to the interior of the 

 last half of the last whorl, and thus creates an open cavity into which 

 water may enter freely to bathe the gills. The mantle is thicker at its 

 lateral and anterior edges. Interlacing blood vessels and longitudinal 

 muscle fibers are conspicuous. 



The anterior border bears a series of large, projecting, fleshy papil- 

 lae, the farthest to the left being the largest. The four papillae far- 

 thest to the left are bulbous at their basal attachment to the mantle 

 and pointed at their distal ends, which may be seen projecting well 

 beyond the edge of the shell. To the right of these are six to eight 

 progressively smaller papillae that are not bulbous at their bases. To 

 the far right and opposite the anal opening is a single, rather long, 

 papilla. Seshaiya (1934, p. 191) , in his work on Paludomus tanschaiu- 

 rica, was of the opinion that "the presence of definite sinuses in the 

 processes in communication with the circumpallial vessel would show 

 that the processes may function to some extent as accessory respiratory 

 organs." I agree with him that in all likelihood such is the function 

 of these papillae. It is significant to note that the largest ones are 

 located on the left side where water flows into the mantle cavity. 

 Seshaiya's contention that these papillae have little or nothing to do 

 with the development of spiral sculpturing of the shell is further sup- 

 ported by the facts that : ( 1 ) The shell-producing area of the mantle is 

 set posterior to the papillae, (2) there is no correlation between the 

 position of the spiral rows of beads on the shell and that of the mantle 

 papillae, and (3) Eemisinus cubanianus (Orbigny), from Cuba, bears 

 papillae very similar to Thiara^ yet its shell is smooth. 



