38 U.S. NATIONAL MUSEUM BULLETIN 284 



attached to the second pterygiophore.) The possibility cannot be 

 excluded, however, that the first dorsal spine's pterygiophore has 

 been lost. 



The dorsal segmented rays are bilaterally paired structures, and 

 each except the terminal is attached to a bilaterally paired distal 

 pterygiophore, which in turn is attached anteriorly to the expanded 

 distal end of the unpaired proximal pterygiophore just anterior and 

 attached posteriorly to a sub terminal prominence of the proximal 

 pterygiophore just posterior. The terminal dorsal ray lacks a distal 

 pterygiophore and is directly attached to the distal end of the terminal 

 proximal pterygiophore. Each spine-bearing pterygiophore and each 

 proximal pterygiophore is attached to a separate neural spine. 



There are two anal spines and 17 segmented rays (range for the 

 species: 14-18; for the genus: 14-20). Each ray is a bilaterally paired 

 structure. The first spine is attached to its own pterygiophore but 

 the second spine is attached to the proximal pterygiophore supporting 

 the first distal pterygiophore and its associated first ray. It may be that, 

 similar to the condition in the dorsal fin, the first spine-bearing pterygi- 

 ophore has been lost and the first spine is attached to the second 

 pterygiophore and the second spine has been shifted onto the proxi- 

 mal pterygiophore of the first ray. The spine-bearing pterygiophore 

 is different in appearance from the ray-bearing proximal pterygio- 

 phores. Each segmented ray except the last two is supported by an 

 unpaired distal pterygiophore, which is attached in turn anteriorly 

 to the expanded distal end of the proximal pterygiophore just anterior, 

 and attached posteriorly to a subterminal process on the proximal 

 pterygiophore just posterior. The terminal two anal rays lack distal 

 pterygiophores, and both are attached to the distal end of the terminal 

 proximal pterygiophore. In some specimens of E. nigricans (and 

 other species of Entomacrodus) the terminal two proximal pterygio- 

 phores each support a single ray and in this condition only the last 

 ray lacks a distal pterygiophore. 



The two pterygiophores supporting the first and second anal spines 

 are attached to the posterior surface of the first haemal spine. The 

 remaining proximal pterygiophores are attached each to a separate 

 haemal spine. 



Pectoral and Pelvic Girdles and Fins 

 FiGxmE 12 



Each posttemporal is dorsoventrally forked and has a tube for a 

 sensory canal passing through the bone between the forks. The 

 sensory canal from the posteriorly directed arm of each lateral extra- 

 scapular passes into the canal of its respective posttemporal. The 



