V i°s\ X l Shufeldt on a Hybrid Grouse. 283 



So far as my observation goes, such hybrids usually stand 

 more or less intermediate in size between the parent birds. 

 This appears to have been the case, judging from the trunk 

 skeleton, with the hybrid Grouse now under consideration. A 

 few measurements will show this, and they are given in the sub- 

 joined table. 



*s s v v v. 



-» 3 -» -2 -* -2 « .. S tf * , 



Adult specimens 

 (Measurements in millimetres.) 



Tympanuchus americanus 



Hybrid 



Pediocajtes p. campestris 



In my osteology of the Tetraonidoe, above cited, I have 

 already shown that the cervico-dorsal chain of vertebras consists 

 numerically of fifteen leading cervicals, if we so designate them, 

 followed by four dorsals that are fused into one piece, and 

 finally a single free dorsal standing between this piece and the 

 pelvic sacrum. This is precisely the arrangement in the verte- 

 bral chain of the trunk skeleton of the hybrid Grouse we are now 

 examining. They are characteristically tetraonine, and are each 

 somewhat larger than the corresponding ones in the spinal 

 column of Pcdiocivtes p. campestris. But the vertebral ribs of 

 this hybrid, with their costal ribs, are distinctly more like those 

 of the Sharp-tailed Grouse (Pcdioccctcs) than they are like the 

 ribs in Tympanuchus. My Hayden memoir calls especial 

 attention to the peculiar form of the ribs of the species of the last- 

 named genus of Grouse, in that they, as well as the epipleural 

 appendages they support, are markedly broad and spreading. 1 

 This is not nearly so much the case in Pedioccvtcs nor, as I 

 have just said, in this hybrid bird. 



Passing next to the pelvis, we meet with a very interesting 

 structure, to the student of the morphology of birds, and it would 

 indeed be hard to conceive of a bone that in its form stands so 

 directly intermediate between the pelvis of Tympanuchus and 

 Pedioccctes. This is the more easily appreciated inasmuch 

 as in the former genus a pelvis is met with that is strikingly dif- 



1 Osteology of the Tetraonidce. Hayden's 12th Annual Report, U. S. Geol. and 

 Geograph. Surv. of the Territories, 1882, p. 680, Plate XI, figs. 79, 80. 



