GORILLA. 65 



impressed ; the last whorl is more constricted, and suddenly 

 widens towards the a]ierture, becoming again constricted behind 

 the peristome, and it is more deeply deflected iu front ; the mouth 

 is much less oblique, the palatal folds are longer and more 

 flexuous, and the tooth on the basal edge of the peristome is 

 longer and more quadrate ; in this latter respect, as well as in 

 contour and shape, it more resembles C. odoniophora. [Fig. 20 h 

 shows the barriers from behind, a piece of the shell-wall having 

 been broken away.] A reference to fig. 20 a, which exhibits the 

 parietal folds, will explain why the upper fold is invisible from 

 the aperture, being hidden by the median fold with which it unites 

 about the middle. Figs. 19 6 and 19 c show that the palatal folds 

 are distinctly visible through the shell-wall. The specimens de- 

 lineated in figs. 19, 20, and 21 are all mature and being composed 

 of five whorls, it follows that the barriers are placed near the end 

 of the fifth whorl. In fig. 20 c the second palatal fold is shown 

 by itself, the upper convex line indicating its attachment to the 

 siiell-w^all. 



a b c 



Fig. 20. — CoriUafrijfP. 



An im.raature specimen was found to contain five palatal plates 

 in the fourth whorl, the upper four being much broader and more 

 elevated than those in mature shells, reaching nearly to tlie inner 

 wall ; they overlap, being placed close together, slanting obhquely 



Fig. L'l. — Corilla fri/ce, immature, X -• 



upwards, but scarcely curving ; the fifth (lowest) is very short 

 and narrow and corresponds in position to the fourth fold in the 

 full-grown shells. Fig. 21 shows the four upper plates as seen 

 through the shell-wall. A still younger shell received from the 

 late Mr. Collett possessed a set of these immature barriers at the 

 beginning of the third whorl, a short distance from the nepionic 

 part of the shell, demonstrating that the animal begins to form 

 these structures almost directly after being hatched. 



