1870.] 5 [Bliss. 



This interneural spine, which is small and thin, expands at its 

 upper extremity into a thick, superiorly arched plate which forms a 

 part of the nuchal shield. Anteriorly this plate is united by sutures 

 to the supraoccipital and parietal bones. Posteriorly it is embraced 

 by the two anterior branches of the dermal plate belonging to the 

 second interneural spine. Cuvier, Meckel and others, have described 

 this plate as a lateral expansion of the top of the first interneural 

 spine, affirming that this spine had no corresponding fin ray. This 

 seems to me, however, to be incorrect, for this plate, although in 

 many species closely united to the interneural spine, appears to be, 

 in reality, a modified dermoneural spine — the first spine of the 

 dorsal fin, — thus altered from its normal form to constitute a part of 

 the defensive armor of the neck, An examination of our common 

 Amiurus catus tends to confirm this view; for in that species the 

 homologue of this plate is not soldered to the upper end of the 

 interneural spine, but rests loosely upon it; showing that it is a dis- 

 tinct bone. 



This plate, above described, exhibits every variety of form in the 

 different members of the Doras and Siluroid families. In some it is 

 very large, and forms a prominent bone in the nuchal shield. In 

 others, as in Oxydoras, it is a slender, lozengershaped piece inters 

 calated between the supraoccipital and the large plate of the second 

 interneural spine. In many Siluroids it is removed from the cranial 

 bones, uniting only with the supraoccipital at its posterior extremity, 

 This is the case in Perinampus typus. In Amiurus catus we find 

 it reduced to its minimum of development, and hidden under the 

 thick skin of the body. 



The second centrum is six times as long as the first, and carries an 

 anterior and posterior pair of parapophyses, not united together at 

 their bases, as is the case in many Siluroids. The anterior pair of 

 these apophyses consist of thin, vertically expanded plates, arising in 

 common from the centrum and the neural spine above, and expand- 

 ing at their extremities into porous spatulate discs, to which the 

 anterior portion of the air bladder is attached. Ordinarily in the 

 Siluroids the extremities of these apophyses are not thus modified, 

 but unite by synarthrosis with the suprascapula. Between the cen- 

 trum and the bases of these apophyses are found, on each side, three 

 small curiously shaped bones united to one another and to the cen- 

 trum by ligaments. Posteriorly these bones afford attachment to a 

 portion of the investing sheath of the air bladder. The anterior 



