440 PEOF. C. STEWAET ON THE MEilBEANOUS 



municated by a common fissure-like opening witli tlie sacculus. 

 This fissure was 15 mm. in length, commencing in. a point 

 posteriorly and gradually widening to 3 mm. in front. It 

 probably represented the canalis utriculi anterior, ductus utriculi, 

 and canalis recessu-saccularis found in certain other Sharks, but, 

 owing to its character, I shall speak of it as the fissura utriculo- 

 sacciilaris. 



The posterior utricle presented the usual characters and 

 communicated by a round hole, about 2 mm. in diameter, with 

 the saccule in front. 



The saccule and lagena were both of large size and with the 

 external face directed outwards and forwards. 



The nerve-supply of the ampullae was of the usual amount, that 

 of the recessus moderate in quantity, the sacculus and lagena 

 being very slightly supplied. The long nerve from which 

 branches are given off to the saccule and lagena ran first of all 

 upwards and then dipped downwards to supply the ampulla of the 

 posterior canal, lying in the latter part of its course on the 

 external surface of the utriculus posterior. Immediately before 

 passing behind this structure it gave ofi" the ramulus neglectus. 



The sacculus and lagena were filled with a perfectly colourless 

 and transparent mass of mucin of a firm jelly-like consistence, in 

 which the otoconia (moderate in amount) were imbedded. 



Immediately behind the small o^Deniug in the cartilaginous 

 cranium, through which the ductus endolymphaticus passed, 

 was an oval deficiency in the skull closed by tough fibrous 

 membrane ; it led directly into the large space in which the 

 dorsal end of the posterior utricle and commencement of the 

 posterior canal were lodged. It measured 17 mm.Xll mm., its 

 long axis being parallel with the posterior canal. 



A similar opening has often been described in other Elasmo- 

 branchs, and is referred to in a paper by the late Prof. G. B. Howes 

 ia the Journal of Anat. & Physiol, vol. xvii. 1883, p. 188. 



Cesteacion philippi. Pam. Cestracionidse. (PI. 44. fig. 2.) 



The specimen from which this labyrinth was obtained measured 

 about 100 cm. (3 ft. 4 in.) in length. 



In proportion to this size the labyrinth is small and the otoconia, 

 if present, scanty. The chief peculiarity of the labyrinth lay in 

 the ductus endolymphaticus. This passed through a long canal 



