XX 
INTRODUCTION. 
homologous -with the “ iliac,” is not only of great length, hut has 
also sharply reflected extremities, which seem to have been originally 
Fig. A. 
Pelvic cartilage of Cyclobatis oligodacfylui. — Senonian, Mount Lebanon, hp., 
basil cartilage of pelvic fin ; il., iliac process ; ph., pubic cartilage ; ppb-, 
prepubio process. [From Proc. Zool. Soc. 1888, p. 128.] 
in direct connection with the distal end of tho pectoral meta- 
pterygium. 
Median Fins. 
A Lower Carboniferous species of Splienacanthm (p. 242) presents 
as highly specialized an arrangement of the median fins as most 
modern Sharks ; but in the primitive Chondrenchelys of the same 
age, and in the late Palaeozoic Pleuracanthus, a lower stage of 
development persists. In Chondrenchelys there was evidently a 
long undiflerentiated median fin, with at least one series of slender 
supporting cartilages above the neural spines. In Pleuracanthus 
(according to C. Brongniart) a long dorsal fin is separated from the 
diphycercal caudal ; and there is also said to be a small separate 
“ cephalic ” fin supported by the barbed spine — a feature of which 
the spine itself affords no evidence. As pointed out by R. Kner ‘, 
the series of interspinous cartilages supporting the dorsal fin is 
double ; and C. Brongniart shows these elements to be twice as 
numerous as the neural arches, each of the neural spines distally 
bifurcating to support them (see fig. B, p. xxiv). Very striking in 
Pleuracanthus, on the other hand, is the specialization of the median 
'■ Sitzung.sb. math.-naturw. Cl. k. Akad. Wise. Wien, vol. Iv. (1867), pis. i., 
