1770 Bulletin 4-7, Uyiited States National Museum. 



based exclusively on cranial characters, summarizes what has been said 

 and includes some details not hitherto mentioned : 



a. Base of skull markedly curved. Interorbital space convex or flat, broad, less than 

 3^ in tbe base of the skull. Processes of inesetlimoid not directeu upward. 

 Ventral process of basisphenoid rudimentary. Cranial ridges obsolete or weak, 

 spines absent or delicate. 

 6. Cranial ridges (except parietal) obsolete or very slightly developed. Cranial 

 spines absent or very inconstant and weakly developed. 

 c. Parietals not meeting; mesethmoid processes weak and depressed; skull 

 moderately thick; parietal ridges weak, with minute spines or none; 

 other ridges none, 

 d. Interorbital space plainly convex. paucispinis. 



dd. Interorbital space nearly flat. johdani; goodei. 



ce. Parietals meeting in the middle line, but separated p'>steriorly by a wedge- 

 shaped exposure of the supraoccipital. Mesethmoid processes better 

 developed, straight, and horizontal; skull thick, the bones striated; 

 parietal ridges low, spineless, other ridges none. 

 e. Preociilar spines none. flavidus; mklanops. 



ee. Preocular spines present. mystinus. 



hh. Cranial ridges somewhat developed; preocular, supraocular, postocular, tym" 

 panic, and parietal spines present, all delicate; ventral process of basi- 

 sphenoid sometimes present in young. (Tympanic spines usually absent or 

 imperfect in atrovirens.) 

 f. Parietals not meeting ; -interorbital sj)ace usually plainly convex ; bones 

 thick, more or less striated. 

 g. Supraocular spine present. 



h. Base of skull strikingly curved; parietals nearly meeting. 



ENTOMELAS; OVALIS ; HOPKINSI. 



hh. Base of skull less strikingly curved ; parietals well separated. 

 i. Interorbital plainlj' convex. pinniger. 



ii. Interorbital space flat, or nearly so. miniatus. 



gg. Supraocular spine absent ; parietals well separated ; interorbital space 

 but little convex ; mesethmoid processes directed somewhat up- 

 ward. ATEOVIRENS. 

 aa. Base of skull markedly curved. Interorbital space flat or slightly concave, of 

 medium width, 3J to 4^ in base of skull. Processes of nie.sethmoid directed 

 but little upward. Ventral process of basisphenoid rudimentary or fairly de- 

 veloped. 

 j. Cranial ridges fairly developed ; supraocular spines absent ; skull thin, papery ; 

 mesethmoid processes horizontal. 

 k. Parietals not meeting. saxicola. 

 kk. Parietals meeting. DIPLOPBOA. 

 aaa. Base of skull nearly straight (slightly curved) . Interorbital space flat or slightly 

 concave, of medium width, 4 to 4i in base of skull. Processes of mesethmoid 

 directed but little upward. Ventral process of basisphenoid rudimentary or 

 poorly developed. Cranial ridges and spines quite strong. 

 I. Cranial ridges well developed. Preocular, supraocular, postocular, tympanic, 

 parietal and nuchal spines present; coronal spines usually present. 



INTEONIGER; AURORA; MELANOSTOMrs. 



aaaa. Base of skull straight, or nearly so. Interorbital space concave and narrow, 4J 

 to 6^ in base of skull. Processes of mesethmoid directed upward. Ventral 

 process of basisphenoid well developed. Cranial ridges high and strong. 

 m. Supraocular spine present. Parietals not meeting. 



n. Skull thick; cranial ridges l)r()ken into tubercles and spines; inter- 

 orbital space fiat ; mesethmoid processes horizontal ; ventral process 

 of basisphenoid rudimentary in adult (the skull of young almost 

 exactly as in ro«act'M«; see below), rubebrimus. 



