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a certain distance between the orbits, for in addition to the proötic, sphenotic (postfrontal, Ridewood) 

 and supraoccipital, Ridewood says tliat the alisphenoid, and even the orbito-sphenoid form, in one 

 or other of the fishes described, a part of its floor. 



Dr. E. C. Starks, of Stanford University, having most kindly sent me two specimens of Elops 

 and a few specimens of Albula, I have examined the temporal fossa in both of these fishes. In Elops, 

 I find that the posterior portion only of the fossa is the homologue of the entire fossa of Scorpaena. 

 This posterior portion of the fossa is mueh shorter and much less important than the anterior portion, 

 and is separated from the latter portion by a wide and evenly rounded transverse elevation of the 

 floor of the fossa. This transverse elevation, or saddle, separates the fossa into two portions, which 

 have the appearance of having been primarily more or less independent, and only secondarily united 

 to form a single continuous groove. The anterior portion apparently corresponds to the anterior 

 divertieulum of the temporal groove of Amia, the posterior portion corresponding to the temporal 

 groove itself of that fish. 



The lateral wall of the posterior portion of the fossa is formed by the pterotic and opisthotic, 

 its mesial wall by the epiotic and supraoccipital, and its floor by the pterotic, the exoccipital, and the 

 temporal interspace of cartilage. In the mesial wall of this posterior part of the fossa there is a deep 

 depression which is certainly the homologue of the preepiotic fossa of Ridewood's descriptions of 

 Clupea, though that author does not, in Elops, so dehne it. 



The saddle between the anterior and posterior portions of the. fossa is formed, in Elops, mainly 

 by the pterotic, the saddle arching over the subtemporal fossa and forming its roof. On the summit 

 of the saddle the layer of bone separating the two fossae is so thin that a slight further excavating of 

 the bone, on either side, would break down the bony separating wall and either put the two fossae into 

 direct communication, or leave them separated by membrane only. This latter condition is said by 

 Sagemehl ('91, p. 555) to be found in Rasbora and Leptobarbus of the Cyprinidae. 



The floor and side walls of the anterior portion of the fossa are formed by the pterotic, proötic, 

 sphenotic and alisphenoid, the part of the alisphenoid here concerned being a part of a well developed 

 flange on the internal surface of the bone together with that part of the internal surface of the bone 

 that lies postero-lateral to that part of the flange. This flange of the alisphenoid is continuous ventrally 

 with a ridge on the internal surface of the proötic, this ridge forming the anterior wall of the labyrinth 

 recess. The anterior semicircular canal, running upward and laterally, lies postero-lateral to the 

 ventral portion of the flange, in a recess in the alisphenoid, and, as this recess is bridged by a narrow 

 bar of bone, the dorso-anterior end of the semicircular canal lies in a short canal in the alisphenoid. 

 The sphenotic comes into no bounding relations to the labyrinth recess, being wholly excluded from 

 it and also from all bounding relations to the cranial cavity, by the deep anterior portion of the tem- 

 poral fossa. If this condition of the sphenotic is primary, its bounding relations to the anterior semi- 

 circular canal aie evidently a secondary acquisition, and that the condition is primary would seem 

 to be indicated by its being found in this primitive teleost, in Amia, and also in Esox. In neither 

 of these three fishes does the bone extend through the cranial wall; and it accordingly must have been 

 first developed, wholly independent of the anterior semicircular canal, simply to strengthen the post- 

 orbital process of the skull and to give a proper surface of attachment to the muscles that have their 

 origins there. A similar origin is ascribed by Gaupp ('03) to the autopterotic in Salmo. 



In the deepest point of the anterior portion of the fossa there is, in the proötic bone, a small 

 circular opening. From this opening a canal runs at first downward in the proötic to the dorsal edge 



Zoologica. Heft 67. 2 



