CHAPTER XIII 
PHTHINOBRANCHII: HEMIBRANCHII, LOPHO- 
BRANCHII, AND HYPOSTOMIDES 
UBORDER Hemibranchii.—Still another transitional 
3 group, the Hemuibranchii, is composed of  spiny- 
rayed fishes with abdominal ventrals. In this sub- 
order there are other points of divergence, though none of 
high importance. In these fishes the bones of the shoulder-girdle 
are somewhat distorted, the supraclavicle reduced or wanting, 
and the gill structures somewhat degenerate. The presence 
of bones called interclavicles or infraclavicles, below and behind 
the clavicle, has been supposed to characterize the order of 
Hemibranchit. But this character has very slight importance. 
In two families, Macrorhamphoside and Centriscide, the inter- 
clavicles are absent altogether. In the Fistulariide@ they are 
very large. According to the studies of Mr. Edwin C. Starks, 
Fic. 180. Fig. 181. 
Fic. 180.—Shoulder-girdle of a Stickleback, Gasterosteus aculeatus Linn:eus. 
(After Parker.) 
Fie. 181.—Shoulder-girdle of Fistularia petimba Lacépéde, showing greatly ex- 
tended interclavicle, the surface ossified. 
the bone in question is not a true infraclavicle. It is not identical 
with the infraclavicle of the Ganoids, but it is only a backward 
extension of the hypocoracoid, there being no suture between 
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