2GO 



NEW YORK STATE MUSEUM 



them of a large ramal vacuity in either ramus of their lower jaws. 

 Then their tympanic bullae are of a more shell-like form, and 

 more prominent. Especially is this the case in Canachites 

 canadensis. Otherwise the skeletons are quite similar to that 

 of G . bankiva, and the departures from it are of a very in- 

 significant character. The body of the sternum is somewhat broader 

 in the grouse, but the best distinctive character is met with in the 

 form of the pelvis, for that bone in Canachites is considerably 

 broader and more shallow than it is in the wild chicken. 



It is no less remarkable than it is beautiful to discover these close 

 resemblances in skeletal structure in birds coming from countries so 

 widely separated, though it is the cause of no surprise to the 

 ornithotomist, who fully appreciates the fact that such is ever the 

 case with forms more or less closely affined, and typical representa- 

 tives of the group to which they severally belong — come from any 

 part of the world they may. 



Any of the species of the genus Bonasa possess a skeleton which 

 is particularly noted for being more delicate in structure than any 

 of the other grouse. All the bones of the skull in Bonasa 

 umbellus [pi. I, fig. 2] are markedly slender and light, and the 

 rounded, bulging basis cranii strongly remind us of the correspond- 

 ing area or region among the Perdicinae. Its zygomata, maxillo- 

 palatines, palatines, and premaxillaries are all delicately propor- 

 tioned. In the trunk skeleton, the limbs of the os furcula are also 

 very slender comparatively, although the hypocleidium is large. 

 The body of the sternum is very narrow as it is in Gallus [pi. 5, 

 fig. 23], while its xiphoidal prolongations, especially its innermost 

 pair, are reduced to the very slimmest of proportions. The usual 

 bones for a grouse are in it pneumatic, and the pneumatic foramina 

 are large. The pelvis in this bird has the general form of that bone 

 as we found it in Canachites, but is relatively somewhat more nar- 

 row and rather longer. Its walls are thin in comparison, and con- 

 sequently the entire structure is lighter. 



Of all our Tetraoninae I consider the representatives of the 

 genus Bonasa more nearly related to the Perdicinae than any of 

 the other grouse in the avifauna of this country. My convictions 

 on this point, however, have been reached chiefly through my studies 

 of the osteology of the forms we have under consideration, but I be- 

 lieve they will be supported, when a critical comparison comes to be 

 made, by the remaining systems of their economy. 



