1 82 AMERICAN JOURNAL 



The distortion alluded to consists of sudden enlargement of 

 the whorl near the aperture, something like Planorbis cam- 

 panulatus, in consequence of which the animal has been 

 unable to continue the usual sutural line, the upper margin of 

 the whorl diverging from the prior one, and making a canali- 

 culate suture. 



Remarks on the Habits of Spirialis Flemingil* By 



Alex. Agassiz. 



" They come to the surface of the water about an hour after 

 dusk; they do not remain long, and after ten o'clock at night 

 were rarely met with. He succeeded only once in finding a 

 few isolated specimens during the heat of the day ; while at 

 full tide, soon after dark, they were very often found in abun- 

 dance. These animals are very easily kept in captivity, and 

 their habits, which can then be carefully watched, may explain, 

 in a very satisfactory manner, their sudden appearance and 

 disappearance. As was already previously known, these ani- 

 mals can creep about by means of their wing-like appendages. 

 When kept in captivity, it was noticed that they but rarely 

 left the bottom during the clay, merely rising a few inches and 

 then falling down again to the bottom of the jar. After dark, 

 however, they could all be seen in great activity, moving near 

 the surface of the water as fast as their appendages enabled 

 them. During the day they often remain suspended for hours 

 in the water simply by spreading their wing-like appendages, 

 and then suddenly drop to the bottom on folding them. This 

 habit of remaining at or near the bottom, which they have in 

 common with so many of our marine animals, explains un- 

 doubtedly their appearance and disappearance, as they proba- 

 bly only come to the surface in search of food at certain hours. 

 When the animal is in motion, beating the water like a butter- 

 fly to propel itself forwards or upwards, the shell is carried at 

 right angles, hanging somewhat obliquely to the direction of 

 the movement. To counterbalance this weight, an exceeding- 

 ly long and powerful siphon extends on the opposite side of 

 the animal, which is used as a kind of balance-wheel, the 

 shell, while the animal is in motion, assuming a totally differ- 

 ent position when it is not thus counterbalanced. Mr. Agas- 

 siz exhibited at the same time drawings of the animal in dif- 

 ferent attitudes." — Proceedings Boston Soc. Nat. History, p. 

 15, Sept., 1865. 



* This species occurred in great abundance at Nahant during the sum- 

 mer of 1863. It is the first time that a living Pteropod of this family has 

 be3n observed on this coast. 



