Transactions of the Linnean Soviely. 261 



rows, &c. Ill these the pair of muscles which descend along the trachea, 

 divide at a short distance above its end, and send one portion to be 

 inserted upon the posterior end of the first bone of the bronchi, and 

 another portion to be inserted in front below the extreme point of the last 

 bone of the tube. Within the angle formed by the separation of these 

 two muscles, a third slender muscle arises, which is inserted upon the 

 sternum. The fourth arises near the middle of the bottom of the tube and 

 is inserted, near the first, on the extremity of the first half-circular bone. 

 The fifth, arising from the same situation as the fourth, is directed down- 

 wards and forwards, and is inserted upon the last bony ring of the tube, 

 on the cartilaginous projection immediately below it, and on the extreme 

 end of the firstbronchial bone. The tension given by these muscles produces 

 variation both in the diameter and the length of the bronchial tube; but 

 its influence is inferior to that exercised by the apparently less compHca- 

 cated organ of the Parrots, vvhere the lower insertion of the shortening 

 muscle of the bronchi, and the power of altering the size of the aper- 

 ture, more than compensate for the smaller number of muscles with which 

 these Birds are provided. 



In " A Synopsis of the Testaceous Pneumonobranchous Mollusca 

 " of Great Britain : by J. G. Jeffreys, Esq.," the authour has given a 

 complete species, so far as they are yet known, of our native land and 

 fresh-water univalve shells and their inhabitants. To the latter he has 

 especially attended, and he has, in almost every instance, succeeded in 

 observing and briefly describing them. On them too he has chiefly 

 founded his larger groups ; a correct principle which augurs well for his 

 future exertions in the department of nature to which the present paper 

 refers. There is something curious in viewing Mr. Jeffreys' Synopsis, in 

 connexion with other papers on the same subject which have appeared 

 from time to time in the Linnean Transactions: it shows most forcibly the 

 advance of the principle of subdivision so universally adopted by modern 

 zoologists. In the excellent Catalogue of British Testacea by Dr. Maton 

 and Mr. Rackett, nearly the whole of those univalves which inhabit the 

 land and the fresh-water were referred to the single genus Helix, Linn., 

 the remaming few were placed in the genera Turbo, Foluta and Patella. 

 The same plan was adopted more recently by the Rev. R. Sheppard in his 

 list of the species found in the County of Suffolk ; but in this an advance 



