no. 3647 PERCIFORM FISHES — GOSLINE 55 



The other two main series of the Blennioidei rarely are flattened 

 anteriorly, generally tend (for very different reasons) to reduce the 

 number of pelvic rays, and, with the exception of the Leptoscopidae, 

 never have the pelvics widely separated. 



Of these two series, the Zoarceoidae, so far as known (but see 

 below) , are structurally the most homogeneous. There is among the 

 zoarceoids a general trend toward elongation, and concurrently (as 

 noted) for the pelvic fins, followed by the pectorals, to diminish and 

 disappear. In skull characters, the zoarceoids are all specialized: 

 there is no separate, medial extrascapular; the prootic always is 

 excluded from the orbital border by the parasphenoid (fig. 106) ; and 

 there is no basisphenoid. In this last feature, the zoarceoids differ 

 from all but a few of the other Blennioidei. The single nostril on 

 each side of the head will distinguish immediately the zoarceoids 

 from all tropical Blennioidei. 



The trachinoid-blennioid-congrogadoid series is internally diverse. 

 It is defined more easily in terms of lack of peculiarities that the 

 notothenioid and zoarceoid lines have developed than in terms of its 

 own specializations; nevertheless, there are two weak trends of 

 development that may be noted for the trachinoid-blennioid-con- 

 grogadoid series. The first trend is toward a consolidation of the 

 bones of the circumorbital ring. Trachinus (fig. 7c) and the con- 

 grogadoids are the only members of the Blennioidei with a well 

 developed percoid-type subocular shelf, and from here there is usually 

 a further fusion of circumorbital elements, rather than a disintegra- 

 tion of the circumorbital ring that tends to occur in the zoarceoids 

 and notothenioids. This differentiation in circumorbitals, however, 

 is not constant (see above). The second trend seems to be a tendency 

 in the Trachinidae, Uranoscopidae, Dactyloscopidae, and tropical 

 blennies to erect the close-set pelvics and use them as props under 

 the body. This trend, however, does not extend to the Leptoscopidae, 

 Congrogadidae, and Notograptidae. 



If the specializations held in common by the trachinoid-blennioid- 

 congrogadoid series are unimpressive, those that differentiate the 

 three components of the series are well marked. In the first place, 

 the three groups making up the series appear to have very different 

 modes of life. The trachinoids, made up of the Trachinidae, Urano- 

 scopidae, Leptoscopidae, and Dactyloscopidae, partially bury them- 

 selves in sand or mud (Gill, 1907) and apparently wait for or positively 

 attract passing prey. Of the various morphological characteristics 

 related to this habit, only one associated with respiration need be 

 noted here. The gill covers extend down over the branchiostegal 

 membranes, which are completely free from each other and from the 

 isthmus (see p. 43). In the tropical blennies and congrogadoids, by 



