9(^ 



The following are the dimensions of the parts. 



Auditory cavity, ant. post, diam 4,5 cm 



„ „ vertical „ 3,5 „ 



„ „ transverse „ 3,0 „ 



Utriculus, including recessus, length . . . . 0,8 „ 



Sinus superior, length vertically 1,2 „ 



Canalis ant., length incl. ampulla 5,7 „ 



,, post., „ ,, „ 5,0 „ 



„ ext., ,, „ „ ",* „ 



Ampulla anterior, length 0,4 „ 



It is difficult to measure the semicircular canals accurately, and 

 the anterior and posterior canals probably do not differ in length. 

 Together with the sinus superior they practically equal the horizontal 

 canal. 



The following features then are remarkable in the membranous 

 labyrinth of this fish. 



I. In the complete conjunction of utriculus and sacculus, that is 

 to say in the absence of any distinction of pars superior 

 and inferior, it differs from all other fishes (putting out of 

 account the Cyclostomata) except the Lophobranchii ' ). 

 II. But in the lack of separation between sacculus and lagena, it 

 is of simpler construction even than the two Lophobranchiate- 

 genera whose auditory organ has ben studied. In this respect 

 it is approached, though not equalled, by its close allies Ostra- 

 cion and Tetrodon, in both of which according to Retzius (though 

 not in the Lophobranchii) the communication between sacculus 

 and lagena is wide and open instead of being by a narrow 

 foramen or duct. 



III. It agrees with the four genera above mentioned, and diliers from 

 other Teleostei in the absence of a macula neglect a. 



IV, The general proportions of the labyrinth are unusual, the semi- 

 circular canals being disproportionately long, and the vestibule 

 very small. 



V. Orthagoriscus is also exceptional among Teleosteans in lacking 

 the usual solid otoliths, and in possessing instead numerous small 

 otoconia, compacted together, but still distinct even to the na- 

 ked eye, as in Elasmobranchs. 

 Dundee, Nov. 26. 1887. 



1) See Retzius on Siphonostoma and Hippocampus, Gehör- 

 org. d. Wirbeltiere, I, 1881, pp. 98 — 100. 



