Skull o/Gonorliynclius Grovi. .'JG.'J 



when all the characteristic features of Gonorhijnckun cxce|)t 

 the extension of scak^s over the head iiad ah'eady l).;eii 

 acquired. The genus iXotogoaeus of the freshwater Eocene 

 deposits of North America and Europe differs from the 

 recent Gonorhynchus only in the absence of pterygoid and 

 lingual teeth, the shape of the subopercular bone, and thy 

 position of the dorsal tin (see Smith Woodward, Proe. Zool. 

 Soc. 1896, pp. 5O0-5U4-, and 13. M. Cat. Foss. Fishes, iv. 

 p. ix). 



The cranium of Gonorhynchus Greyi (PI. XVI. figs. 2, 3, 

 and 4) is long and flattened, and in the ethmoid and orbital 

 regions rather slender. The frontals form nearly the whole 

 of the roof of the cranium and exhibit no median suture. 

 Tiie parietals are separated by the supraoccipital, and extend 

 back to cover the epiotic prominences ; the tubular scales of 

 the transverse commissure of the sensory-canal system are 

 readily removable from the parietal and supraoccipital bones, 

 upon which they are set. The exoccipitals fail to meet above 

 the basioccipital, so that the foramen magnum is not bounded 

 by the exoccipitals alone. The foramen for the passage of 

 the vagus nerve is remarkably large. 



The cranium articulates with the vertebral column by a 

 hemispherical head, which is not removable, and consists of 

 a portion of a vertebral centrum fused with the basioccipital 

 and lower parts of the exoccipitals. This convexity of the 

 occipital articulation is not peculiar to Gonorhynchus, for 

 Owen and Klein have recorded it in Fistularia (Anat. of 

 Vert. i. 1806, p. 107, and Jahresh. Wurtt. 188J, p. 325), 

 aud Klein in Synynathus, Phyllopteryx, Gastrotokeus, and 

 Ostraciun (Jahresh. Wiirtt. 1885, p. 108). The most 

 recent observations are those of Starks, who states that 

 the basioccipital condyle is a round knob in the families 

 Fistulariidae and Aulostomidie (Proc. U.S. Nat. AIus. 

 XXV. 1902, pp. 619-634). 



The ascending wings of the parasphenoid rise high ; they 

 pass up in front of the pro-otic and come into contact with 

 the alisphenoid and postfrontal of each side. The para- 

 sphenoid fails to reach as far back as the posterior end of the 

 basioccipital; the eye-muscle canal does not open poste- 

 riorly; neither the i)arasphenoid nor the vomer bears teeth. 

 The alisphenoidsare widely separated, and there is no orbito- 

 sphenoid nor basisphenoid. The ethmoidal region is long, 

 and the mesethmoid, which is small and flat, is separated 



2:>* 



