FISHES OF FAMILY BLENNIIDAE 23 



The ringlike jointing surface of each pterotic's pyramidal section 

 joins its respective sphenotic dorso-anteriorly, prootic ventro- 

 anteriorly, exoccipital ventroposteriorly, and epiotic dorsoposteriorly. 

 Some portion of the synchondral joints with each of these four bones, 

 except the sphenotic, is visible on the external surface of the skull. 

 Dorso-anteriorly, each pterotic overlaps its respective frontal (but 

 the anteriormost tip of the pterotic passes under the frontal), overlaps 

 portions of the dorsal and posterolateral surfaces of its respective 

 sphenotic, and is overlapped ventrolaterally by its respective inter- 

 calar (a portion of the intercalar may also insert in a pocket on the 

 pterotic external surface). 



The posterior end of each pterotic's bladelike portion is raised 

 dorsaUy into a thin crest that is continuous with a crest formed by 

 its respective parietal. Just ventrolateral to the pterotic crest is 

 the fossa in which the posterior dorsal condyle of the hyomandibular 

 articulates. Extending posterolaterally from the fossa is the expanded 

 pterotic "spine." A ridge on the ventral side of the spine is contin- 

 uous with a ridge on the surface of the intercalar. A broad ligament 

 arises from the ridge (both portions) and attaches to the dorso- 

 anterior surface of the cleithrum. The ventral arm of the posttemporal 

 is attached by a short ligament to the area where the ridges of the 

 pterotic and intercalar meet. A slender dorsal projection of the 

 proximal portion of the pterotic spine exists posterior to, and slightly 

 separated from, the lateral end of the raised crest of the pterotic's 

 blade-like portion, thus forming a U-shaped groove. A branch of the 

 laterosensory canal passes through this groove to the preopercle. 

 The 1-shaped lateral extrascapular at its anterolateral angle has 

 an opening that faces the internal margin of the groove. The internally 

 directed arm of the 1-shaped extrascapular lies against the posterior 

 surface of the pterotic crest. The posteriorly directed arm of the 

 extrascapular lies on top of the pterotic's thickened pyramidal 

 portion, and obscures the pterotic-epiotic joint in this region. 



Anteriorly, on the internal surface of the pterotic blade, there is 

 a broad, shallow groove for the pterotic canal of the laterosensory 

 system (the internal waU of the groove is formed by the sphenotic). 

 The groove becomes a tube in the bladelike portion at about the 

 midlength of the blade and continues posteriorly, opening externally 

 just posteroventral to the lateral end of the pterotic crest. The 

 pterotic canal here continues into the anterolateral opening of the 

 lateral extrascapular. Internally, the pterotic's pyramidal portion 

 contains a U-shaped canal that surrounds the horizontal semicircular 

 canal of the ear. 



Sphenotic (figs. 1-4). — ^Each somewhat paddle-shaped sphenotic 

 gives rise on its posteroventrolateral border to the upper half of 



