188 Seientific Proceedings, Royal Dublin Society. 



first, but more curved and far more slender ; it articulates below, 

 but in contact with, the second epipleural spine, with a groove on 

 the postero-inferior surface of the parapophysis of the fourth ver- 

 tebra (PL YIII., fig. 19). The third rib is similar, but more on the 

 posterior border of the parapophysis ; the fourth rib and epipleural 

 spine are in contact for a shorter distance, and the parapophysis 

 being longer, the two bones are removed farther from the body of 

 the vei-tebra ; the sixth rib and epipleural spine do not come in con- 

 tact, the former being nearer the tip of the parapophysis ; behind 

 this they get farther apart, the ninth rib being about half an inch 

 from the epipleural 'spine. All the ribs behind the fifth articulate 

 with the posterior borders of the parapophyses (which are generally 

 grooved for them) — the neck of the rib only articulating, and the 

 head projecting into the lateral muscle. 



The epipleural spines are curved bones resembling the ribs, but 

 stronger; the anterior nine being large (If to 2 inches), but be- 

 hind this they diminish rapidly, and disappear about the four- 

 teenth. The first is supported entirely by the first rib, and the 

 next four partly by rib and partly by parapophysis ; behind this 

 they articulate with small depressions about the middle of the 

 posterior border of the parapophyses. Their direction is upwards, 

 backwards, and outwards. 



The Inierspinous Bones and Fin-rays. — The general form of an 

 interspinous bone (interhsemal or interneural) is a straight (some- 

 times curved) rod of bone, joined above at an obtuse angle with 

 a thicker piece ; the latter is hollowed at the end, and contains 

 cartilage, which is prolonged into a rounded knob which supports 

 the fin-rays; near the superior extremity of the bone in front is 

 a saucer-like depression, formed by a prominent fiange of bone; 

 this supports the cartilaginous head of the interspinous bone in 

 front and its articulation with the fin-rays. The first and second 

 (most anterior) interneurals are very large, and expanded from 

 before backwards, being the result of the fusion of several indi- 

 viduals. 



The above description applies to the dorsal and anal fins ; in the 

 caudal fins there are no interspinous bones (unless the hypural 

 bones be regarded as such),^ but in its anterior part there are 



^ " Generally the kypurals are the interspinous bones alone, the arches being here 

 obsolete" (Macalister, op. cit. page 7i). 



