/. — Pleuracanthidce. 723 



of Newcastle-on-Tyne. It exhibits a part of the body and the posterior portion 

 of the head, with a number of teeth. Several detached cranial plates (5, h) and a 

 large bone (a), which probably represents the lower jaw, are present. Associated 

 with these are many spinous and interspinous bones. The latter are long, straight, 

 and slender ; of a dense bony structure, apparently similar to that of the spines. 

 The spinous apophyses are much dilated at the proximal extremity, which was 

 attached to the sheath of the notochord (c, c). The teeth are those of the so 

 named. Diplodus gibbosus, medium size ; the lateral prongs are slender and 

 attenuated, and the median denticle is also comparatively long. 



The long interspinous rays are frequently met with in the coal fields where 

 remains of Pleur acanthus occur. On PI. Lxxi. two interspinous rays are figured, 

 natural size; one measuring 0" 12m. and the other 0'125m. Along with these 

 were found examples of the surapophyses, three of which are represented on the 

 same Plate (fig. 4). They vary from 0-01 to 0*015 m. in length. 



A specimen exhibiting the left pectoral fin is represented on PI. lxv., fig. 2. The 

 part preserved is O'l m. in length, and comprises a portion of the pterygium, 

 with a mass of fin-rays attached to its outer border, and a smaller series on its 

 inner one. The constitution of the central axis is not well preserved. The outer 

 series of fin-rays number in this specimen twenty-two or twenty-three ; the 

 longest are 0'09 m. in length, and each is divided into about ten parts articulated 

 together. The articulated segments are longest in the median part of the ray, 

 shorter towards the axis, and pointed at the distal extremity ; they have an average 

 diameter of 0"002m. The rays are semi-osseous, and have the usual granular 

 appearance. The fin-rays springing from the inner surface are shorter and more 

 slender ; they are little more than half the diameter of those on the opposite one. 



The form and constitution of this fin differ considerably from those described 

 by M. Brongniart* and Dr. Fritsch.f There are a larger number of rays, and 

 each is divided by a greater number of articulations. The rays attached to the 

 segments of the pterygium, near the basal extremity, are proportionately longer 

 than those of the French or Bohemian fishes. 



The specimen figured is from the cannel coal at Tingley, in the West Eiding 

 of Yorkshire, and is in the collection of the writer. 



* Etudes teiT. houil. Commeiitry, p. 25, pi. it. 



f Fauna der Gaskohle Bohmens, vol. ii., pt. it., p. 99. 



