244 PROCEEDINGS OF THE ACADEMY OF [1893. 



are almost always in this condition, and it may be impossible to 

 know whether they originally had such ribs or not, if they be of a 

 form not represented in the recent fauna. 



It seems that there are also differences in the surface sculpture of 

 the nucleus or the (about 1}) embryonal whorls. While in the rib- 

 less species — V. pulchella, excentrica, declivis — it is, as a rule, 

 smooth, the ribbed V. costata and related forms have it marked 

 with fine, rather dense revolving, raised lines (Man. Conch.. PL 33, 

 fig. 54), about 10 or less, on the visible part. Whether they are 

 also present below the periphery of the embryonal shell I am 

 unable to say. 



Habits of the animals. — I have seen living specimens only of V. 

 pulchella, excentrica, costata, alhula and perspectiva (of the latter only 

 one). They were kept in confinement for weeks. As we find 

 mature and young specimens at all times, it seems that their propa- 

 gation, as well as the duration of life, are not bound to a certain 

 season. Their movements are slow and somewhat unsteady — evi- 

 dently it is not easy to carry the comparatively large and heavy shell. 

 It occupies 15-30 seconds in transversing a space corresponding 

 to the diameter of the shell. They shun light decidedly, as do most 

 of our North American land snails. I repeatedly observed individ- 

 uals, when brought into day- or lamp-light, moving slowly with 

 head and disc only a little projecting, the eye peduncles quite short ; 

 when they were shaded, the latter stretched out and the motion 

 grew more lively ; when in full light again, the animal became 

 evidently uneasy, made a few quicker motions, and changed its 

 direction. It was generally several seconds before perception was 

 followed by motion. To judge also from other experiments, sight 

 seems to be very imperfect. It is not only in this group of molluscs, 

 but in others, quite unlike the sense of feeling, which is more acute. 

 The heart is, as in other mollusca, strongly influenced by tempera- 

 ture and the degree of general activity or rest. In a temperature 

 of about 50-60° F., it contracts at a very slow rate, about 20- 

 25 per minute, but variously in different individuals, as will be seen, 

 from the following observation : Of two mature V. pulchella lying 

 on the table at a temperature of about 65° F., one had the heart 

 contracting 72, the other 32 times per minute; after they had been 

 on my warm hand for about two minutes, the heart of the former 

 made 110, of the latter 68 contractions per minute. They are able 

 to live under water for a considerable time, even for several hours ; 



