PYGOPTERUS GREENOCKII, ETC. 703 



any such division takes place. The fulcral scales of the anterior margin are not 

 seen, being obscured by the matrix. 



The dorsal fin (fig. 1, D), measuring 1 inch 8 lines in breadth at its origin, is 

 placed very far back, being nearly opposite the anal, and consists approximately 

 of about 45 rays, which are rather coarse in the anterior two-thirds of the fin, 

 but become finer posteriorly. The transverse articulations of the individual rays 

 are rather close together, but the joints are still longer than broad, and the whole 

 ray bifurcates a little beyond its middle. Fine, closely set fulcral scales are 

 observed along the anterior margin of the fin. 



The anal fin (fig. 1, A), like the dorsal, is large and strong; its base measures 

 1 inch 9 lines across. As in the latter, the transverse articulations of the rays are 

 approximated; the joints of the first transverse row are, however, nearly twice 

 as long as broad. The anterior margin is, as usual, set with small fulcral scales. 



The caudal fin (fig. 1, C) is by far the largest, and, as far as its lower lobe is 

 concerned, the longest of the azygos fins, the portion preserved of this lower lobe 

 being, in the specimen figured, If inch long at its anterior margin ; and we may 

 safely suppose it to have been originally at least § of an inch longer. It is, how- 

 ever, the worst preserved of all the fins of the specimen, so that all attempts to 

 count its rays are in vain. These are somewhat finer than those of the dorsal 

 and anal fins ; their transverse articulations are much approximated, so that the 

 joints are almost square. The stouter rays of the front of the lower lobe are not 

 seen to bifurcate so far as they extend, till cut off by the edge of the nodule ; the 

 succeeding finer ones begin to split about their middle. The rays of the upper 

 lobe are too badly preserved to admit of description, further than that they are 

 comparatively short, and very fine. The tail, as a whole, is most typically hetero- 

 cercal, the extremity of- the body being continued along the upper lobe of the 

 caudal fin, where it is defended by the tAvo kinds of scales, lateral and mesial, 

 already described . 



On examining another specimen, not figured, I find that the rays of the caudal 

 fin, like those of the anal of Poli/pterus, commenced below the skin in narrow 

 flat pieces, imbricating from before backwards, and not divided by transverse 

 articulations. 



Internal skeleton. — I have in no instance found any trace of vertebral bodies, 

 but, scattered among the scales of disjointed specimens, may often be seen pointed 

 bony fragments, which must be the remains of the vertebral apophyses. 



The intersjrinous bones of the azygos fins seem to have been well developed, 

 as shown in a specimen not figured, but already referred to in the description of 

 the rays of the caudal fin, and in which these bones, supporting the anal and 

 caudal fin, are seen together, with traces of those belonging to the dorsal. 



In connection with the anal fin, I counted at least 15 of these bones, which 

 are very strong in front, the anterior one measuring 11 lines in length. They 



