Dr. R. H. Traquair on Harpacanthus. 493 



Pores scattered through a distinct dermal membrane. Skele- 

 ton : — {a) dermal, an irregular feltwork of slender cylindrical 

 spicules ; (b) main, a reticulation of large acerate spicules, 

 with fibres distinct in parts. Spicules : — (1) smooth, slightly 

 curved cylindricals, size '48 by '012 millim., chiefly dermal ; 

 (2) long, smooth, curved acerates, sometimes sharp and some- 

 times blunt, size "9 by '025 millim. ; (3) a very small and 

 slender sceptrella-like spicule, consisting of a slender shaft, 

 bearing two saucer-Hke whorls near tiie base, with very 

 slightly denticulated margins, length "037 millim., diameter 

 of larger (upper) whorl '0125 millim. Occurring scattered, 

 chiefly in the dermal membrane. 

 Locality, Station 135 ?, 60 fath. 



Eeratum, — We find that the generic name Troclioderma (p. 344, 

 suirra) has been already used ; we therefore propose instead the name 

 Axoniderma, from Greek a^wj', a wheel (type species Axoniderma mirabile, 

 Ridley and Deudy). 



XLV. — On Harpacanthus, a new Genus of Garhoniferous Sela^ 

 chian Spines. By Dr. R. H. Teaquaie, F.R.S., F.G.S. 



Under the name of TristycMus Jimbriatus a small but inter- 

 esting Selachian spine from the Carboniferous Limestone of 

 Gilmerton, near Edinburgh, was described and figured by 

 Mr. T. Stock in a paper " On the Structure and Affinities of 

 the Genus TristycMus ^^^ published in this journal three years 

 ago *. 



The spine is described as being 1| inch in length ; it is 

 tolerably slender, and, according to the figure, is pretty 

 sharply curved backwards beyond the middle. " Its surface 

 is smooth 5 but a shallow and wide groove occupies a nearly 

 central position along the middle third of the spine." Poste- 

 riorly it shows along its distal fourth seven strong, pointed, 

 recurved denticles, in connexion with which the writer remarks 

 that " the second row (if existent) is concealed in the matrix." 

 The walls are described as being " apparently thick and the 

 pulp-cavity small," and it is further stated that the inserted 

 portion of the spine is not preserved. 



* Ann. & Mag. Nat. Hist. (5) xii. pp. 177-190, pi. vii. 



