FISHES OF FAMILY BLENNIIDAE 27 



ExocciPiTAL (figs. 2-5). — Externally each exoccipital contacts its 

 respective prootic anteriorly and anteroventrally, its pterotic and 

 epiotic dorsally, the supraoccipital dorso-anteromesially, the opposite 

 basioccipital dorsoposteromesially, overlaps the parasphenoid ventro- 

 mesiaUy and joins the first vertebra ventroposteriorly. It is externally 

 overlapped by its respective intercalar medio-anteriorly. (Variably 

 a shallow pocket may be present on the external surface of the ex- 

 occipital into which a portion of the intercalar's posterior margin 

 may insert.) 



Ventrally, on its internal surface, each exoccipital has a ventro- 

 anteriorly extending laminar projection, which joins the basioccipital 

 on the projection's ventral margin — the main waU of the exoccipital 

 also joins the basioccipital on the exoccipital's ventral margin; thus, 

 a shallow anteriorly open pocket in the exoccipital, floored by the 

 basioccipital, is formed. Internal and for the most part anterior to 

 the projection is the posterior portion of the concavity, formed with 

 the posteroventral portion of the prootic. The posterior portion of 

 the sagitta rests dorsally internal to this concavity. A secondary, 

 circular concavity exists posteriorly in this exoccipital concavity and 

 is mostly dorsal to the level of the laminar projection. The lapUlus 

 rests partly over the anterior portion of the secondary concavity. 

 It seems probable, because of the shape and size of the two concavities, 

 that in life the sagitta and lapiUus fitted neatly into these concavities; 

 the laminar projection would then act as a retaining device covering 

 the inner surfaces of the ventroposterior end of the sagitta and the 

 ventral end of the lapiUus. These otoliths and the sacculus and utri- 

 culus probably were displaced slightly in preservation and subsequent 

 clearing and staining. 



Both dorsal and posterior to the level of the just-discussed con- 

 cavities of each exoccipital, there are two ridges, in line but extending 

 in different planes, on the internal surface of the exoccipital. The 

 pterotic's ventral margin and the prootic's postero-internal margins 

 join the ventro-anterior ridge, and the epio tic's ventroposterior mar- 

 gin joins the long dorsoposterior ridge. The pterotic and epiotic form 

 a joint that is perpendicular to the level of the two exoccipital ridges 

 and dorsal to the narrow space separating the ridges. Ventral to the 

 area of separation of the two exoccipital ridges is a relatively large 

 and deep concavity. In the area of this concavity the membranous 

 horizontal and posterior vertical semicircular canals of the ear join. 

 The horizontal canal passes through a tube of bone extending some- 

 what dorso-anteriorly from the concavity. The walls of this tube are 

 formed by the exoccipital and pterotic posteriorly and the pterotic 

 alone anteriorly. The vertical canal passes through a tube of bone 

 extending somewhat dorsally from the concavity. The walls of this 



290-282—68 3 



