348 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. WolYl. 



resenting tlie caudal vertebrae, and we have in our possession a pelvis of 

 this bird where a rudimentary second sacral rib is evident, but this can 

 only be regarded in the light of an anomaly. 



Interesting osseous malformations are occasionally to be seen, but they 

 are beyond the jurisdiction of this monograph to treaty nor will it be 

 practicable to enter into the engaging subject of the differences between 

 the pelves in the male and female birds, but that such differences do 

 exist there can be no reasonable doubt. 



Did classification depend entirely upon external topography, appear- 

 ance, and structure, the author would say that the North American Tetra- 

 onincB as they now stand are well classified; but strip them of these char- 

 acteristics, or, rather, permit them only to hold the subordinate place, 

 allow specific habits to have no weight, and then from an osteological 

 point of view, purely, we can perceive no good reason why Pedicecetes 

 and Cupidonia should not be thrown into one and the same genus. As far 

 as their skeletal framework is concerned they are singularly alike, and 

 strikingly dissimilar from all the other genera ; but as such changes will 

 only be generally suggested and tolerated as our knowledge of ornithot- 

 omy increases, it must of necessity remain to be seen how the anatomy 

 of the other systems of these two birds will support such a generic 

 reduction. 



Fort FETTEEiiiAN, Wyc, May 1, 1881. 



EXPLANATION OF PLATES. 



PLATE V. 



Fig. 47. — Cranium of young Centrocerctis, three or four days old, viewed from above. 



Fig. 48. — The same; lateral view, with lower jaw added, showing articular element 

 detached. 



Fig. 49. — The same, viewed from below. 



Fig. 50. — Centrocercus. Lateral view of skull of " bird of the year" four months old; 

 the hyoid arch has been detached. 



Fig. 51. — The same aged bird as in Fig. 50, showing the disarticulated segments of 

 the four cranial vertebrae : OV, neural arch of the occipital vertebra (epencephalic 

 arch), first of the skull; OV, its haemal arch in outline (scapular arch); so, super- 

 occipital; eo,exoccipital; po, the connate paroccipital; 5o, basi-occipital; PV, neural 

 arch of the parietal vertebra (mesencephalic arch), second of the skull; P. V.', its haemal 

 arch (the hyoideau); P, the parietal; ms, the mastoid; as, the alisphenoid; hs, the 

 basi-sphenoid ; gh, the glossohyal ; ch, the ceratohyal ; ih, the basi-hyal ; «//, the urohyal; 

 hi and cb, the hypo-branchial and cerato-branchial elements of the thyro-hyals, 

 respectively ; F. V., neural arch of the frontal vertebra (proencephalic arch), third of 

 the skull; F.V.', its haemal arch (the mandibular) ; Fr, the frontal; x, the site of the 

 postfrontal in some of the class; os, the orbito-sphenoid in outline; ps, the basi-pre- 

 sphenoid ; Tp, the tympanic ; ar, the articular ; S. an, the surangular ; an, the angular; 

 se, the splenial element ; and de, the dentary element ; N. V. , the neural arch of the 

 nasal vertebra (rhinencei)halic arch), the fourth and last in the skull ; N. V.', its haemal 

 arch (the maxillary) ; N, the nasal ; Pf, the prefrontal (ethmoid) ; Vr, vomer in out- 



