52 Lamarck's Genera of Shells. 



summit, slightly pointed at the base ; elevated on a fleshy ten- 

 dinous pedicle, fixed to marine substances. Hinge without teeth. 



The animal of the lingula has two arms, and, according to 

 Cuvier, two hearts. Its two arms are opposite, very long, 

 fleshy, not articulated, fringed on one side through their 

 whole length, extensible beyond the shell, and rolled up in a 

 spiral form when drawn in. 



Only one species. Lingula anatina* . (Patella unguis. Linn.) 



Shell greenish, resembling in form a duck's bill. Pedicle 

 cylindrical, from two to four inches long. 



Molucca Seas. PI. II. Fig. 105. 



Note. — We are indebted to our accurate friend Mr. G. B. Sowerby, for 

 pointing out a mistake which Lamarck has fallen into, in asserting all the 

 shells of the family .ircocea to be marine. (See our last Number, p. 317.) 

 Nueula rostrata, helonsive: to the '1th genus of the Arcacea, {Area rostrata, 

 Gmel.) is called by ScTiroter, Area fluviatilis, and he says that " it is found 

 in the rivers of the Coromandel coast!" (See Schrbter's Naturgeschiste der FIvss 

 Conchylien, 1779.) Mr. Sowerby adds, that he believes there are several 

 other rirer arks, but none of them are described by Lamarck, unless A. se- 

 nilis be, as he suspects, a river-shell. 



Art. VI. On a Mode of protecting the Specula of Re- 

 flecting Telescopes. 



[In a Letter to the Editor from Dr. Ure.] 

 My dear Sir, 



I HAVE at present in my possession an excellent seven feet 

 reflecting telescope, of nine inches aperture, mounted on the 

 plan of the late Sir William Herschel's, but furnished with a 

 curious mechanism for covering up the mirror very closely, 

 or uncovering it, without opening the tube at the lower end, 

 as is necessary in using Sir William's. By this means, it is 

 completely protected from suffering by moisture in dewy nights, 

 an accident which we cannot avoid, by carrying the instrument 

 into an apartment before covering the mirror ; for its relative 

 coldness generally causes an immediate deposition of vapour 

 on its surface in such circumstances. The mirror of the ten 

 feet Herschelian belonging to the Glasgow Observatory, was 

 injured one evening in this way. The following letter and 



tAdj. from anas, a duck. 



