94 



aud giviug some of its dimensions, and also calling attention to the 

 presence of three semicircular canals instead of two as had formerly 

 been described. 



The auditory labyrinth of Orthagoriscus is very peculiar, and 

 differs more or less from that of all other Teleostean fishes. It hangs 

 suspended by webs of delicate connective tissue within a wide space, 

 continuous with the brain-cavity, very much as in Chimaera, according 

 to Retzius' description. A single vertical pillar of cartilage passes 

 down across this space, within the arc of the horizontal canal. (In 

 Hakting's specimen another passed within the arc of the anterior vertical 

 canal). After removal of the membranous labyrinth no distinct grooves 

 or impressions remain in the cartilage capsule to indicate the former 

 position of the parts within it. 



In the membranous labyrinth of Orthagoriscus the following parts 

 are distinguishable : Utriculus with Sinus superior, Re cess us 

 utriculi, the three semicircular canals with their corresponding am- 

 pullae, and the Sacculus and Lagen a hardly separated from one 

 another or from the Utriculus. Six nerve-endings are visible, three 

 cristse ampullarum, macula recessus utriculi, maculae sacculi and la- 

 genas ; but I sought in vain for the macula neglecta. The Utricu- 

 lus is a roundish sac, passing gradually in its upper part into the 

 thin-walled conical Sinus superior, which terminates by bifurcating 

 into the anterior and posterior canals, without extending into any 

 free „apex" between them. Anteriorly it opens into the wide recessus 

 utriculi from which it is marked otf by a scarcely notable constriction : 

 at the base of the latter cavity is a well-marked and ratter large ma- 

 cula recessus, opposite which is a little pouched diverticulum. The 

 recessus is connected above with the ampulla anterior and externally 

 with the amp. externa, w^hich both open somewhat widely into it. The 

 amp. posterior, rather more perfectly formed, opens by a narrow neck 

 into the hinder part of the utriculus, just above the entrance into it 

 of the horizontal canal. The sacculus and lagen a form a single com- 

 mon cavity, and are only entitled to the retention of their names by still 

 possessing their separate nerve-endings. They are neither separated 

 from one another nor from the utriculus, of which they simply form a 

 slightly bulging expansion on its inner side. The inner or median wall 

 of the sacculus bears near its lower part a rather large roundish 

 macula; posterior to which is a smaller vertically elongated nerve-en- 

 ding, corresponding to the papilla lagenae. I could not find a 

 trace of the ductus endo-lymphaticus. 



No otoliths of the kind usual in Teleosteans exist, but instead the 



