/. — Pleuracanthidce. 711 



of Cestracion, except that it is in a more advanced position. The dorsal fin 

 extends the whole length of the back to the base of the caudal, equal to 

 three-fifths the entire length of the fish. The dorsal fin, as previously shown 

 by Kner* in specimens from Klein-Neundorf, is supported by a complicated 

 series of rays. The bony neurapophyses are broad at the base, forked above ; 

 to each branch of the fork is attached a short ray, the surapophysial, to which 

 is attached the interspinous ray supporting the fin-ray. The caudal fin encircles 

 the posterior extremity of the body. Its upper lobe is supported by a series 

 of rays similar to those of the dorsal fin, except that the surapophyses are absent ; 

 and nearer the extremity the interspinous bones also disappear. The hsema- 

 pophyses are more robust and longer than the neurapophyses, but have no rays 

 attached : the first five or six hsemal arches are composed of two parts, united 

 at their base and encircling the notochord. Further back they diminish in 

 length and lose this character. The scapular and clavicular elements of the 

 shoulder girdle are cemented into one piece, and their junction forms the point 

 of attachment of the pectoral fin. The central support of the fin consists of a 

 jointed pterygium, the elements composing it gradually diminishing in size, the 

 last being long and filiform. From the external margin of this axis spring the 

 fin-rays, varying in length, and articulated. On the internal margin there is a 

 smaller number of rays, not articulated. M. Charles Brongniart considers the 

 pectoral fin of Pleuracantlms to exhibit characteristics intermediate between the 

 biserial articulated pterygium of Ceratodiis and the pectoral fin of Acanthias 

 vulgaris. The pelvic arch has a general resemblance to the pectoral, but it is 

 smaller. Each fin is attached to a moiety of the arch, similar in form and 

 comparable in parts to the scapula and clavicle of the pectoral arch. The median 

 axis is composed of cylindrical cartilaginous elements placed end to end, but 

 diminishing little, if any, in size, and the fin-rays are attached only to the 

 external margin. The axis, instead of being straight, as in the pectoral fin, 

 is curved and forms the arc of a circle. To the extremity of each axis is attached 

 a piece which can only be regarded as an appendix to the genital organs, 

 similar to the claspers in the sharks, rays, and chimera. These are found 

 only on the male fishes. In the female the pelvic fins are feebler, and the 

 median axis terminates within the membrane of the fin. 



There are two anal fins which have remarkable peculiarities. They are 

 lobate, rounded, contracted at the base, enlarged in the middle, and again 

 contracted towards the extremity. Both fins are similarly constructed. The 

 hsemapophyses to which they are attached are shorter and more inclined than 

 those of the caudal region; they are truncated instead of pointed, and three 



* SitzungsbericMe Kaiser. Akad. Wiss. Wien, vol. Iv., pt. i., p. 540, pis. i.-x. 1867. 



TKAUS. KOI. DUB. SOC, N.S. VOL. IV., PART XIV. 6 M 



