138 GASTEROPOD BIVALVES. 



I had intended to have concluded my account of the 

 Crawlers with this interesting passage, connecting, as it does, 

 the tribe with the swimming Pteropods, but it somehow 

 reminds me that I have omitted to mention that some 

 fluviatile Bivalves, as Cyclas and Pisidium,-j- and some 

 marine species (Kellias, Amphidesmae) allied to them in 

 character and bulk, have the same power as the Lymneae, 

 of ascending to the surface of their ponds, or pools, and 

 traversing them from side to side, in a reversed position, as 

 though they were crawling along a solid plane. 



it was only about the size of a silver groat." See also Landsborough's 

 Excursions to Arran, p. 189 ; and Strickland on the Movements of the 

 Lima, in Mag. Nat. Hist. n. s. i. 28. The Bulla akera, in a young 

 state, has the resemblance of a winged insect, and sports in the water 

 with all the liveliness of a butterfly, forming a pleasing object when kept 

 alive in a glass. 



t Jenyns in Trans. Camb. Phil. Soc. p. 12 of the separate Monograph. 

 Macgillivray's Moll. An. Aberd. p. 251. Mery asserts the same of the 

 fresh-water mussel. Hist, de l'Acad. Roy. des Sc. Nat. 1710, p. 538. 



Addition to note * of page 125. 



In a letter to Professor Owen, in the Report of the Transactions of the 

 Sections of the British Association for the Advancement of Science for 1844, 

 p. 77, Madame Power gives a still more particular account of the locomotion 

 of the Argonaut : " It would be difficult to describe the immense variety of 

 the movements of the Argonauta argo in swimming, dragging, and floating, 

 and it would require a series of drawings to represent them : these move- 

 ments vary according to the fancy or caprice of the animal, or to circum- 

 stances ; for instance, when at the bottom of the water, and wishing to rise 

 or go in any other direction, the only movement it makes is to agitate its 

 siphon, and thus it swims with its body and eight arms hidden in the shell; 

 or it swims with its mantles totally or in part extended over the shell ; or 

 holding a portion of the body mere or less above the shell ; or holding its prey 

 with its arms. The Argonaut also drags itself along the sand, gravel, or mud, 

 at the bottom, or climbs millepores and madrepores in search of mollusks or 

 other nutriment, or when it seeks concealment ; it sometimes anchors by its 

 lower arms, hanging from the shell and attached by their suckers." 



