NATURAL SCIENCES OF PHILADELPHIA. 75 



2. OCEANODftOMA HoRNBYI, Bp. ex Gray. 



This, the second species of the genus, was first introduced by Gr. 11. Gray, 

 in the proceedings of the Z tological Society for 1853, p. 62, under the name 

 of Thalassidroma Hornby:. Judging from Mr. Gray's descriptions -for I am 

 autoptically unacquainted with the species it is entirely congeneric with 

 the 0. furcata, though differing greatly from it in colors. This generic dis- 

 position has been made by Bonaparte, on page 195 of the second volume of 

 his Conspectus. It appears as yet to be an exceedingly rare bird in col- 

 lections : none are contained in the Philadelphia Academy or Smithsonian 

 Institution, or, in fact, so far as I am aware, in any American collection. It 

 uas the front, cheeks, throat, collar round the neck, breast, and abdomen pure 

 white; crown, hind head, a broad band in front of neck, bend of wing- and 

 lesser wing coverts sooty gray : upper part of back gray ; lower part of back 

 and tail ashy gray; greater wing- coverts brownish gray; tertiaries and quills 

 deep black. 



11 Length 8.25 inches, tail 3.75, tarsus 1.00, middle toe about the same. Bill 

 a[ong culmen 8.1 line?, along rectus 10J lines." 



I II. CYMOCHUREA, Coues. 



This, the second genus: of the short-legged acute-clawed group of 

 Procellariea; is most nearly allied to Oceanodroma, having like it a loug 

 deeply-forked tail. It is the genus of which the well known Leach's Petrel 

 is typical; and one to which Melania, Bonaparte, and a new species, about to 

 be described, also belong. With the forked tail and short legs of Oceanodroma, 

 it is distinguished from that genus by its comparatively very much longer 

 wings ; by its larger, longer, much more robust bill, with shorter and 

 straighter nasal tubules : by its radically different pattern of coloration, &c. 



The name ' Thalassidroma" is the one under which this genus is generally 

 presented. Founded by Vigors in 1825, upon the Procellaria pelagica, Lin- 

 nasus, the name has been employed by ornithologists, in a most unaccount- 

 ably loose and vague way, to designate any and all the species of Procellariea;, 

 without the slightest regard to their natural generic affinities. In 1856, 

 Bonaparte first restricted Thalassidroma to a single genus, that one of which 

 Leachii, Temminck, is the type. But if used at all, it must be, of course, for 

 that genus of birds upon which it was founded, viz., the one of which 

 pelagica is the type; for it is contrary to all rule to use a synonym of one 

 genus as the tenable name of another. As will be demonstrated further on, 

 u _ Thalassidroma., Vigors, ' : is a complete synonym of Procellaria proper of Lin- 

 !ia3us, as is also //./.. of Boie, both being based upon the P. pelagica, 



Linnaeus. This being the case, it is evident that the present well known 

 genus has yet to receive a tenable distinctive appellation. 



In supplying a name, I take Leachii, Temm., or rather leucorrhoa, Vieill., as 

 my type; and in the following diagnosis so define the genus as to exclude all 

 forms not entirely congeneric with it. 



Cgmochorea,* Coues. {=Thalassidroma, Bp. nee Vigor.,. Type Procellaria leu- 

 corrhoa, Vieill.) Bill much shorter than^he head, about two-thirds the tarsus, or 

 middle toe with the claw, rather stout, as high or higher than broad at the 

 base, the unguis strong, much decurved; the nasal tubes less than half as long 

 as the culmen. Wings moderately long, not much surpassing the tail when 

 folded; first primary longer than the fourth, second longest. Tail exceed- 

 ingly long, deeply forked, the feathers all broad, their tips obtusely rounded. 

 Legs short; bare space of tibias brief. Tarsus equal to middle toe and claw. 

 of rather large size, and stout form. Colors unicolor, or nearly so. 



Three species are at present known to constitute this genus. These are 

 the following : 



* Etym. from Gr. Ktquox, "way?," and %oos, "a dance". 



1864.] 



