Transactions of the Linnean Society. 261 
rows, &c. In 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 tensiongiven 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 complica- 
cated organ of the Parrots, where 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 remaining few were placed in the genera Turbo, Voluta and Patella. 
The same plan was adopted more recently by the Rey. R. Sheppard in his 
list of the species found in the County of Suffolk; but in this an advance 
