80 AstadUa lomicomis 



&• 



My friend, Mr. W. Baird, discovered this little snail when 

 he was examining some marine Conferva? which had been ga- 

 thered in Berwick Bay. It has a close resemblance to the black 

 slug, and its motions are similar, creeping along the bottom, 

 or swimming on the surface, reversed, with equal ease, although 

 at a slow rate. When disturbed it withdraws the head under 

 the cloak, just as the slug does, and assumes a nearly circular 

 form, which it preserves for some time. It was fond of leaving 

 the water, and crawling a short way up the edge of the saucer, 

 as most littoral Mollusca are. The quantity of gelatinous 

 secretion which oozed from the skin seemed to be unusually 

 great. When it was immersed in fresh water, the wrinkled 

 state of its skin proved that the creature was pained, and it 

 died shortly after, without excreting any coloured liquid ; but 

 after death it exhaled a very perceptible odour, which was pe- 

 culiar and not disagreeable. 



That Limapontia nigra belongs to the gasteropodous Mol- 

 lusca, I entertain scarce a doubt. The consistence and form 

 of the foot, its distinctness from the skin of the back or cloak, 

 the opacity of the body, and the mode of progression, convince 

 me of this ; and an attempt to examine the internal struc- 

 ture showed that there were various distinct viscera, although 

 I could not ascertain their relations and nature : a stomach 

 and intestine, however, were obvious ; but I detected no trace 

 of any structure like a lung or gills, so that the order in which 

 the animal ought to be placed is uncertain. My impression 

 at first was, that I had before me the mollusc of some of our 

 minute internal shells, which seemed to be indicated by the 

 protuberance of the back ; but no shell of any kind could be 

 detected. Limap6ntia appears to me to have a close relation- 

 ship to the Aplysia viridis of Montagu ; and perhaps these, 

 and some other analogous beings, might be collected together 

 to form a separate order of their class, distinguished by the 

 want of gills, whose office the cutaneous envelope probably 

 performs. 



Astaci'lla longico'rnis, in the young state, {fig. 15.) 



I have given (in VIII. 494 — 4960 a description and figure 

 of this singular crustacean, and I return to it, for recent 

 observations enable me to add one or two particulars to its 

 history. The animal creeps by means of the three pairs of 

 posterior legs, aided by the long antennae, which are made to 

 touch the ground so as to support it in front, and drag it in 

 some degree forwards. Its motions in this way are slow, but, 

 on the contrary, it swims rapidly ; the principal organs of 

 natation being the lamellar plates under the tail, for the ante- 

 rior ciliated feet did not appear to be called much into action. 



