Jordan and Evcrmann. — Fishes of North America. 1767 



The characteristic spines and ridges are: The preocular on the anterior 

 superior border of the orbit ; the supraocular, near the edge of the frontal 

 bone above the middle of the orbit; the postocular, bahind the supraocu- 

 lar, aud the tympanic, behind the postocular on the frontal bone near the 

 superior posterior angle of the orbit; and the parietal, present in all the 

 species, a longitudinal ridge on the middle of the parietal bone. Of these 

 ridges all may l)e absent except the parietal, and in the different species 

 iu which they are present differ exceedingly in the degree of their devel- 

 opment. The thickness of the bones of the skull is generally correlated 

 with other characters, rather thin papery skulls bearing strongly devel- 

 oped bony ridges, while thicker and more bony skulls have the ridges low 

 or obsolete. But there are several exceptions to the rule. Other charac- 

 ters at first seem important, but as they occur in a few species only, far 

 apart in the series, they must be regarded as sporadic. Thus nuchal 

 spines are present in &. levis, chlorostictus, aurora, and covstellatus (in the 

 last species connected with a tendency of the ridges to break up into 

 spines and tubercles), but they are inconstant even in the species In which 

 they occur, so that it is doubtful whether they are always present in any 

 species. The coronal spines, likewise inconstant, are usually present in 

 S. aurora, and nearly always present in *S'. auriculatus. 



In some species in which pairs of spines are normally absent, these are 

 sometimes present in a rudimentary or distorted form, either singly or in 

 pairs. Although the paucispinis group is characterized by the absence 

 of the usual pairs of spines in adults, 2 adult paucisinnis skulls had a 

 rudimentary supra- or post-ocular on the left side, and a very young skull 

 of this divisiou had rudimentary tympanic spines on both sides and a 

 jjostocular on the left side; a medium-sized meZawops had a rudimentary 

 right tympanic; and a large one had a jjalr of postoculars and a deformed 

 left supraocular; a young flaridus had a rudimentary right postocular; in 

 an elongatus, in which the supraoculars are normally absent, the spines 

 were still present iu the form of low humps on the ridge ; in another speci- 

 men the supraocular spine was sharp and perfectly distinct. 



Hilgendorf expressed the belief that when 1 of the 3 pairs of spines 

 (supraocular, postocular, aud tympanic) is absent, it is the supraocular 

 aud not the postocular that has disappeared.* This is proved by several 

 series' of facts. When the 3 spines are present together, the distance 

 from the base of the tymiiaulc to the base of the supraocular on the one 

 hand, and the distance from the supraocular to the preocular on the 

 other hand, are to each other in many species as 1 to 1, varying from 

 this ratio to 1 to 3 in rosaceus; while where 1 of the spines is absent, 

 the relative distances vary from 3 to 10 to 3 to 15 (except nebulosus, 2 to 5). 

 These measurements give the all but invariable rule that, when 1 of the 

 spines is absent the so-called supraocular occupies the position of the 

 jjostocular. When both the supraocular and postocular are present and 



* Hilgendorf: Uebersicht liber die lapanischen Sebastea-Arten, Sitzunga-Bericht der 

 Gesellschaft Naturforschendeu Freunde zu Berlin, 21. Dec, 1880, p. 168. "Das maximum 

 von Doruen am Oberkopf kommt bei .S'. marmoratus vor, niimMch einer in der Nasenge- 



tend, der nasaldorn, drei aiif dem Augenrand, Orbital-domen, vondenen dermittlere bei 

 en anderu Arten zuerst verachwindet." 



