584 CALIFORNIA ACADEMY OF SCIENCES. l6 



and narrow interorbital space, from mesethmoid processes 

 depressed to those directed forty-five degrees above the 

 dorsal plane of the skull, from a rudimentary to a fully 

 developed ventral process of the basisphenoid and from 

 nearly obsolete to strongly developed cranial ridges. 



The single species ruberrimus furnishes at different 

 stages in its development a series of characters that paral- 

 lel in a striking way the series just described. The very 

 voung skull is so much like those of rosaceus and rho- 

 dochloris that, if it were the only ruberi'imus at hand, it 

 might easily be put between them in a series. The width 

 of the interorbital space is 6y into the base of the skull, 

 relatively narrower than that of any other skull in the 

 collection of fifty, and deeply concave; the mesethmoid 

 processes are directed upward and the ventral process of 

 the basisphenoid is well developed. The very large skull 

 of the same species is almost exactly adapted to the de- 

 scription of the aurora-introniger group. The inter- 

 orbital space is perfectly flat and 4A into the base of 

 the skull, the mesethmoid processes extend forward nearly 

 horizontally and the ventral process of the basisphenoid 

 is rudimentary. The gap between these two extremes is 

 completely closed by skulls of intermediate age. 



S . saxicola and difloproa constitute another interme- 

 diate group with the base of the skull markedly curved, 

 the interorbital space slightly convex or flat, of medium 

 width, 2H to 4^ into the base of the skull, mesethmoid 

 processes directed but little upward, and the ventral pro- 

 cess of the basisphenoid rudimentary or fairly developed. 

 This intermediate group, unlike the other, lacks the su- 

 praocular spine and probably forms one of the links be- 

 tween the entomelas-^pinniger group and the other rock- 

 lisli in w r hich the supraocular is wanting. 



The following classification, based exclusivelv on era- 



