620 Bulletin 47, United States National Museum. 



head about equal to diameter of eye, its length a little greater thau post- 

 orbital part of head. Lateral line well developed anteriorly, becoming 

 obsolete at a distance from end of dorsal about equal to 2i times head. 

 Color uniform light brown ; under side of gill covers dark, showing dark 

 at the edges of the opercular bone. Type 17 inches long. (Named for 

 Dr. Theodore Gill, to whose critical insight the advance of systematic 

 ichthyology in America is largely due.) 



Lipogenys gillii, GOODE & BEAN, Proc. U. S. Nat. Mus. 1894 (1895), 469, pi. 18, fig. 3, and in 

 Oceanic Ichthyology, 173, 1895, Albatross Station 2742, Gulf Stream, from a depth of 

 805 fathoms. (Type No. 39212. Coll. Albatross.) 



Order W. XENOML* 



Coracoids represented by a cartilaginous plate, imperfectly divided; 

 pectoral fin without actinosts. Skeleton very thin and papery. Post- 

 temporal imperfectly ossified. Otherwise sssentially as in the Haplomi. 

 One family, confined to the fresh waters of the Arctic regions, a primi- 

 tive type, allied to the Haplomi, but with the base of the pectoral fin 

 extremely simple in structure, (fevoc, strange; w/zof, shoulder.) 



Family LXXXIX- DALLIHLE. 



(THE ALASKA BLACKFISHES.) 



Body oblong, covered with small, partly embedded cycloid scales; 

 lateral line rudimentary; a line of mucous tubes below eye. Eye small; 



*Dr. Gilbert has examined the anatomy of Dallia, and makes the following observations: 



"The characters assigned by Dr. Gill to his order Xenomi, of which Dallia is the sole repre- 

 sentative, seem to need some modification. The group is thus defined by him: 



"'Teleosts, with the scapular arch free from the cranium laterally, and only abutting on it 

 behind, coracoids represented by a simple cartilaginous plate without developed actinosts, and 

 with the intermaxillary and supramaxillary bones coalescent.' 



"The last of these three characters we have not been able to verify, as the premaxilla, 

 while lying closely appressed to the maxilla, is readily separated from it, the two being in no 

 sense 'coalescent.' The expression 'scapular arch free from the cranium laterally' refers to 

 the simple nature of the post-temporal, which is attached, as usual, to the epiotic, but seems at 

 first sight to lack entirely the inner fork to join the parotic process of the cranium. Closer 

 examination shows, however, that a strong ligament replaces the lacking arm, and answers to 

 it in all its relations. We find, furthermore, that while extending in some specimens the entire 

 distance between the opisthotic and the simple post-temporal, in others the outer portion of the 

 ligament is more or less ossified, the bony rod thus formed being an integral part of the post- 

 temporal, and representing the proximal portion of the missing fork. As stated, this ossifica- 

 tion invades the ligament to a varying extent in different specimens. In at least two which 

 have come under our observation, the fork of the post-temporal thus formed has extended 

 almost the entire distance across to the opisthotic, the shape and relations of the bone being 

 then entirely normal and usual. It is evident that this character is not of high taxonoinic 

 value, and would not of itself warrant any very wide separation of Dallia from what are appar- 

 ently its nearest relatives. The case is different, however, when we come to examine the cora- 

 coid portion of the shoulder girdle. As stated by Dr. Gill, we deal here with a cartilaginous 

 plate in which no ossifications occur, and which is followed immediately by the fin rays, with- 

 out the intervention of actinosts. This coracoid cartilage is an extremely thin and delicate 

 imperforate lamina, usually exhibiting very distinct division into upper and lower halves, 

 which may be taken to represent the hypo- and hypercoracoid elements. In its distal third, 

 the plate begins to break up, by longitudinal subdivision, into a fringe of narrow cartilaginous 

 strips. These approximately equal in number the pectoral rays, and join the latter directly, 

 the basal portion of each pectoral ray forking slightly to receive the tip of the cartilaginous 

 strip. 



"In the deep-sea spiny eels of the genus Notacanthus, there is a somewhat similar condition of 

 the coracoid elements, inasmuch as the hypo- and hypercoracoid, though present, are merely 

 shell-like rudiments surrounded by cartilage, and the actinosts are geatly reduced. It seems 

 probable that we are dealing in the two cases with independent degenerations of the shoulder 

 girdle, and that the two groups are not really related." (Gilbert, MS., September 20, 1894.) 



