26 Mr. Strickland's Commentary 



turelles.' The South American species which is there treated 

 of seems to be in several points even more nearly allied to the 

 Cartilaginous Fishes than that from Africa, particularly in 

 the structure of its almost cartilaginous skeleton, and in the 

 spiral intestinal valve, which, from additional observations 

 made by MM. Bibron and Milne Edwards, appeared to be 

 still more developed than in the L. annectens. But it has 

 been found to differ from the last, and from Fishes, in an im- 

 portant particular, that of the heart possessing a double auri- 

 cle ; and also in the rays of the tentacles being of one piece, 

 and not jointed. The structure of the nostril we consider as 

 entirely analogous to that of the organ in Fishes : it is not a 

 respiratory organ in L. paradoxa, the double opening is only 

 similar to the valvular separation of the sac in Fishes, and, 

 from the structui'c of the muscles, would seem to act some- 

 what similarly, and they will cause the passage to resist or pro- 

 mote the flow of the water through it. The position of the 

 opening to the lungs or air-bladder is also of importance in 

 the consideration of this question, and is in favour of its reptile 

 alliance ; but all the modifications of form must be balanced 

 with each other, and additional dissections are required of L. 

 annectens, which it may even yet be found necessary to sepa- 

 rate and place in Mr. Owen's proposed genus Protopterus. 



V. — Commentary on Mr. G. R. Gray's ' Genera of Birds' 

 1S40. By H. E. Strickland, Esq.. M.A., F.G.S., &c. 



[Continued from vol. vi. p. 423.] 



P. 26. The date of Thunberg's genus Brachyurus (1743) seems to 

 be a misprint ; but not knowing in what work it is defined, I am un- 

 able to rectify it. 



Myiophonus ought, I think, to be placed among the Turdin(E near 

 Petrocossyphus. 



The Rock Thrushes were first defined by Boie in 1822, under the 

 name of Monticola, and afterwards altered by him in 1826 to Petro- 

 cossyphus. The former name ought therefore to stand, as authors 

 ought no more to alter their own generic names when once pub- 

 lished than those of others. But should there be any insuperable 

 objection to the name Monticola (of which I am not aware), then the 

 name Petrocincla, Vig., 1825, has the next claim. Bonaparte di- 

 vides the Rock Thrushes into two genera, Petrocincla (P. saxatilis) 

 and Petrocossyphus (P. cyaneus). There seems not to be sufficient 

 ground for this separation ; but if adopted, a new name should be 

 given to P. cyaneus, because the name Petrocossyphus, Boie, is a 

 mere synonym of Petrocincla, Vig., and should therefore be can- 

 celled. 



P. 27. Tardus novcB-hollandicc, Gm., is quoted by Mr. Gray as 



