430 ON THE PETRELS COLLECTED DUE1NG 



Pelecandides is, in some respects, as much specialized as the Albatrosses, 

 though many of its modifications are distinctly traceable to its diving 

 habits, as, e. g., the compressed form of the wing-bones, the great develop- 

 ment of the hypapophyses of the dorsal vertebrae, the elongated sternum 

 and pectoral muscles, the peculiar ribs. But it stands alone (amongst 

 the Procellariidae) in the absence of the ambiens muscle ; the peculiar dis- 

 position of the femoral vein ; the absence of a ballux ; and the single 

 interclavicular air-cell. Moreover, as in Bulweria only of other Tubinares, 

 its myological formula is A.X., there being no accessory head to the femoro- 

 caudal muscle. 

 Zool. Chall. But Pelecandides shows marks of beiog in some respects an early form 



Exp. vol. iv. i n the simple condition of the tensor patagii muscle, in its very simple 

 pt. xi. p. Oo. r J - 



syrinx, and in the general shape of its sternum. It has the characteristic 



form of biceps muscle found in all the Proeellariidse, except the Albatrosses, 

 and like all those forms, except the Procellaria-grou]), has basipterygoid 

 facets. 



Pelecandides is thus, as will be seen, a very well-marked form, though 

 it is somewhat difficult to decide as to whether its peculiarities are such 

 as to entitle it to form a separate subfamily by itself. The presence of 

 basipterygoid facets would seem to indicate that it probably diverged 

 from the general stock of the Procellariinae at a point when the latter 

 had already developed that feature, and therefore at a period after the 

 ancestor of the Procellaria- group in many ways the least specialized, 

 and therefore presumably more ancient, of the subfamily, and in which 

 there are no such facets had already acquired its main characters. 



According to modern ideas, the object of a classification is not so much 

 to represent morphological facts as to indicate the phylogenetic relations 

 of the different forms concerned. According to the first view, Pelecandides 

 might well be placed, as many authors have done, in a special group of 

 its own ; but if we admit, as seems on the whole most probable, that it 

 has been derived from the same stock as the Procellaria-grou]) after the 

 special ancestor of the latter was developed, I prefer considering it as 

 simply a highly specialized form of the Procellariinae. 



The Procellariinae so defined fall into a number of smaller groups, 

 distinguishable by good characters. 



The " Stormy-Petrels " of the genera Procellaria, Cymochorea, and 

 Halocyptena * form one such minor group, distinguished by their general 

 small size and coloration, comparatively long tarsi, nearly single nasal 

 aperture, simple triangular tongue, simple tensor patagii, peculiar skull 

 with no basipterygoid facets or distinct uncinate bone, entire posterior 

 sternal margin, and little specialized syrinx. Procellaria has two ca3ca, 



* Oceanodroma also, I have little doubt, belongs to this group. 



