2298 Bulletin 4.7, United States National Museum. 



America. This family is nearly related to Uranoscopidce, of which group 

 it seems to be a reduced or degenerate branch. Its relations with the 

 Asiatic family Leptoscopidcs are most intimate, the incomplete ventrals and 

 simple pectoral rays of Dactyloscopida; being the chief distinctive features. 

 (Dactyl oscopidcv, Gill, Arrangm. Families Fishes, 1872.) 



a. Dorsal fin divided, the first dorsal composed of 3 spines inserted on the nape; head 

 not cuboid ; chin without flap ; fringes of lips small. GILLELLUS, 852. 



aa. Dorsal fin continuous. 



b. Dorsal fin commencing at the nape; pseudobranchiae very small or obsolete; 

 head cuboid. DACTYLOSCOPUS, 853. 



bb. Dorsal fin commencing far behind the nape; pseudob ranch iie well developed, 

 c. Head cuboid, formed as in Dactyloscopic,- the mouth vertical. 



DACTYLAGNUS, 854. 



cc. Head elongate-conoid, the lower jaw projecting, with a fleshy flap at tip. 



MYXODAGNUS, 855. 



852. GILLELLUS, Gilbert. 



Gillellus, GILBERT, Proc. TJ. S. Nat. Mus. 1890, 98 (semicinctus) . 



A separate dorsal fin on the nape composed of 3 spines. Lateral line 

 descending posteriorly, its dorsal and median portions about equal. 

 Fringes of upper lip obsolete, those of lower lip little evident. Head not 

 cuboid, the mouth moderately oblique, the lower jaw rounded in front and 

 without symphyseal flap. The physiognomy is intermediate between 

 Dactyloscopus and Myxodagnns, from each of which the genus is well sep- 

 arated by the characters of the dorsal fin and the lateral line. ("Named 

 in honor of Dr. Theodore Gill, to whom we owe our knowledge of the pre-' 

 viously described members of this most interesting group." Gilbert.) 



a. Tip of lower jaw projecting. 



&. Anterior portion of lateral line longer than posterior portion ; the scales 25 to 

 28 + 3 + 15 to 18 = 43 to 49. D. III-IX, 28 ; A. II, 30 or 31. 



SEMICINCTUS, 2634. 



bb. Anterior portion of lateral line much shorter than posterior portion, 2^ times 

 in the latter; scales 18 + 3 + 27=48. D. II-IX, 31 ; A. II, 35. 



ARENICOLA, 2635. 



aa. Tip of lower jaw scarcely projecting; anterior portion of lateral line 1J times in 

 .posterior. D. I-IX, 31; A. II, 34. ORNATUS, 2636. 



2634. GILLELLUS SEMICINCTUS, Gilbert. 



Head 3 ; depth 5. D. III-IX or X, 28; A. II, 30 or 31 ; scales 25 to 28- 

 3-15 to 18 (43 to 49 scales in all). Body deep, tapering rapidly either way 

 from front of dorsal. Mouth moderately oblique, the maxillary extending 

 beyond orbit, 3 in head; tip of lower jaw projecting; teeth in a narrow 

 band in front of jaws, becoming a single series laterally; none of the 

 teeth enlarged. Opercular fringes well developed, 8 or 9 in number; fold 

 of membrane between rami of lower jaw well developed; pseudobranchise 

 apparently not developed; gill rakers obsolete. Dorsal fin beginning at 

 a distance from occiput less than diameter of eye, the first 3 rays en- 

 tirely detached from the rest of the fin, the first ray the highest, the 

 second and third shortened; of the remaining part of the fin the first 9 or 



