GALEOMMA. 191 



into delicate fibrous filaments that instantly adhered to 

 the saucer : we detached the animal several times ; the 

 byssus was always left, and a new one formed. On 

 leaving it for the night, in a marked position, we found 

 in the morning that it had detached itself by abandon- 

 ing the byssus, and had formed another at a consider- 

 able distance. The animal marches with great rapidity, 

 by flatting the valves into the form of a circular disk ; 

 it then, by the foot, aided by the muscular margins of 

 the mantle, makes rapid progression. It marched across 

 the saucer before ten could scarcely be counted." Mr. 

 Alder noticed a peculiar expansion of the mantle, which 

 invests the shell like a membrane. Philippi had pre- 

 viously remarked that this membrane resembles the 

 true skin of vertebrate animals ; but Alder has given a 

 further explanation of its structure. He says " it is a 

 continuation of the true skin, and consists of two layers ; 

 the lower of which is slightly muscular, and under the 

 microscope the muscles may be seen interlacing each 

 other in all directions. The outer layer is granular, and 

 is covered with tubercles, which possibly, when the ani- 

 mal is alive, may rise into papilla?. The want of an 

 epidermis appears to be thus supplied." The interesting 

 particulars above given of its organization make us 

 anxious to know more about this wonderful mollusk ; 

 and it is to be hoped that the investigation will be con- 

 tinued by Mr. Alder, or prosecuted by some other ob- 

 servant naturalist. The animal is hardy, and could be 

 safely sent by post, packed in Chondrus crispus or some 

 stiff sea-weed, to any place within reach of the sea. The 

 number, position, and nature of the siphonal tubes have 

 not yet been satisfactorily made out. Philippi describes 

 one only, Mittre two (besides an anomalous organ re- 

 sembling the large tentacle of Lepton squamosum), while 



