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PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 48. 



lateral angle. A minute spine may also be present in the median 

 line directed forward. 



The dorsal fin is inserted normally on the eighth plate of the dorsal 

 series, but may occasionally vary to the extreme posterior edge of 

 the seventh (pentacantTius) , or the anterior edge of the ninth 

 (alascanus). 



The genus is perhaps nearer Bathyagonus than Xeneretmus, 

 agreeing with the latter in the character of the rostral plate, and in 

 the number of predorsal plates. But Bathyagonus is from deeper 

 water, the whole body and the fins are black or brownish black, the 

 mandible is produced beyond the premaxillaries instead of being 

 included within the latter, and the pectoral margin is entire — the 

 lower rays not appreciably lengthened. 



Key to species of Asterotheca. 



a 1 . Plates on cheeks thick, inflexible, immovably united with each other and with 

 the interopercle. Lower 5 pectoral rays thickened. A single median pair of 

 plates in front of ventrals, the remaining plates of median series unpaired (i. e., 

 the plates of the second pair fused). Shallow water species, with comparatively 

 thick plates and heavy spines and ridges, and the lower parts light in color. 

 ft 1 . Margin of preorbital not spinous. Ventrolateral series of plates smooth through- 

 out, without spines; spines of lower lateral series weak or obsolescent, this 

 especially marked on caudal peduncle. A deep nuchal depression. Space 

 between dorsal ridges deeply concave. Plates on cheeks, in adults, without 

 spines or tubercles. Gill-menbranes without posterior free margin. Lower 

 pectoral rays much exserted beyond the membrane, a distinctly deeper notch 

 between the two portions of the fin. No spine on infraorbital ridge below 



front of eye alascana. 



b 2 . Lower margin of preorbital strongly spinous in adults. Anterior plates of 

 ventrolateral series with short but evident spines; lower lateral plates all 

 strongly spinous, except the anterior 5 or 6, which are smooth as in other 

 species. Plates on cheeks with minute spines. A small spine on infra- 

 orbital ridge below front of eye. Nuchal depression shallow. Space between 

 dorsal ridges shallowly concave. Gill-membranes with a narrow free margin 

 posteriorly. Lower pectoral rays comparatively little exserted, no conspicuous 



notch between the two portions of the fin infraspinata. 



a 2 . Plates on cheeks thin, flexible, not fused, readily movable, all (or the posterior 

 two) bearing each a strong backwardly directed spine. Ventrolateral series of 

 plates sharply spinous throughout, as are the lower lateral series, with the 

 exception of the first 5 or 6. Two median pairs of plates in front of ventrals. 

 Lower 4 pectoral rays thickened, a deep notch between the two portions of the 

 fin. A deeper water species, with comparatively thin plates, low ridges, and 

 delicate sharp spines; lower side of trunk and tail dark like the back; eye very 

 large. Spines on eye-ball weak or obsolescent. Palatine patches of teeth 

 narrower than those on mandible pentacantha. 



ASTEROTHECA PENTACANTHA (Gilbert). 



The fin-rays in 18 specimens vary as follows: 





Specimens. 



Dorsal spines. 



VI 

 3 



VII 



11 



VIII 

 4 



Dorsal rays. 



Anal rays. 



7 

 11 



