Bliss.] 8 [June 15, 



formed into an articulating facet, upon which rest the two lateral 

 branches of the third dermoneural spine, and which are kept in 

 position by a pair of muscles extending from the outer edges of the 

 facet to the posterior edges of the arms of the spine. The bone 

 between the facets is hollowed out for the reception of the down- 

 ward projection of the middle portion of the spine. This spine, 

 the third dermoneural, is very large and thick, and has on its ante- 

 rior edge a row of stout conical teeth. The posterior edge of the 

 spine is furrowed and likewise furnished with teeth, but smaller than 

 those in front. The base of this spine is widened and perforated 

 through its centre in an antero-posterior direction. The head of the 

 interneural beneath is united without suture to the second interneural, 

 and to the basal portion of the second interneural crest, and projecting 

 backward as a slender, bent rod, passes through the perforation in 

 the base of the fin-spine, and uniting with the interneural again 

 behind the spine, forms a kind of linked joint. I believe that this 

 kind of joint is formed by the inward projection of the arms of the 

 spine through the crest upon the head of the interneural, and not by 

 an antero-posterior prolongation of the crest through the base of the 

 spine. My reasons for this belief will be made evident in my descrip- 

 tion of the first dorsal fin of Balistes, (see p. 10), where it will be 

 seen that though the interneural crest is completely perforated, the 

 arms of the spine do not pass entirely through it. This peculiar mode 

 of articulation is found in the fishing filaments upon the head of 

 Lopliius piscatorius, in which species the spines of the dorsal fin are 

 modified into long filaments to serve a special purpose 5 1 and whose 

 extreme mobility is secured by the kind of articulation I have"" just 

 described. In the ordinary forms of fin spines, the prolongation of 

 the head of the interneural, which passes through the base of the 

 dermoneural spine behind it, does not unite with the interneural be- 

 longing to the spine through which it passes. But in the Siluroids, 

 as well as in Lophius and Balistes, the use to which the spine is 

 put necessitates this linked-joint mode of articulation. 



The mechanical operation of this complicated apparatus is as fol- 

 lows: the enlarged spine of the fin being used as a weapon of of- 

 fense, the union of the neural and interneural spines with each other 



1 See, Description des filets pecheurs de la Baudroie, par M. Bailly, Annales des 

 Sciences Naturelles, ler, Ser., Tom. n, 1824, pp. 323-332 ; and also, Analogie des 

 Filets Pecheurs, etc., par Geoffrey St. Hilaire, M<5moires du MuseTim d'Histoire 

 Naturelle, Tom. xi, 1824, pp. 132-142. 



