1910.] CAUDAL FIX OF THE TKLEOSTOMI. (517 



agent; thus the last vertebral segment and the last hypurul 

 become one solid structure. Three more hypurals are attached 

 to the last vertebral segment and one is also attached to the 

 preceding centrum. The whole of the dorsal contribution to 

 the caudal fin is supported by four caudal radials. The neural 

 arch to the penultimate centrum is much reduced. Though 

 classified in the same division of Acanthopterygii as Scorpcnna, 

 IVigla provides a striking contrast to this form in the degree of 

 specialization of the caudal fin, being quite a highly specialized 

 type. 



Uranoscopus scaber. (Jugulares, Tra.chinidc'e.) 



The urostyle is absent or indistinguishably fused with the last 

 hypural bone. Hypaxially, the last centrum bears three hypural 

 bones, and epaxially a well-developed neural arch. The pen- 

 ultimate vertebra possesses a hypural bone, but its neui-al arch is 

 greatly reduced ; the antepenultimate vertebra bears both a 

 hypural and epural. Between the epural bone and the neui-al 

 arch of the last centrum are three dorsal caudal radials, while 

 between this same neural arch and the hypural which is fused 

 with the last centrum is a ray-bearing bone which is probably an 

 epaxial element, though situated ventral to the spinal cord, since 

 it is usual for the urostyle to fuse with the last, if any, of the 

 hypural bones. This caudal fin, therefore, attains to a fairly 

 high standai'd of homocercy. 



Oallionymus LYRA. (Jugulares, Callionvmidpe.) (Plate L. 

 fig. 26.) 



The caudal fin of Calllonymus is a very simple type. !fso 

 lu-ostyle is present ; the last vertebral segment has three hypurals 

 firmly fittached to it and to each other, thus forming a single 

 piece, to which dorsally is also fused the neural arch of the last 

 vertebrn. The penultimate vertebra bears an epural {ep.) and a 

 hypural, and one dorsal caudal radial (d.c.r.) is present. 



Cristiceps ARGExrATUS. (Jugulares, Blenniida?.) (Plate L. 

 fig. 29.) 



The urostyle is present only as a small hook embedded in the 

 tissue of the last hypural bone. Hyimxially, the last vertebral 

 segment possesses two hypurals of about equal size, while dorsally 

 it shows traces of two neural arches, thi'ough which the spinal 

 cord passes on its way some distance beyond the end of the axis. 

 The penultimate vertebra posse.sses an epural and a hypural ; 

 posterior to this is a large dor.sal caudal radial. Immediatelv 

 adjoining the distal end of the last hypural, and on its dorsal 

 side, is a small ray-bearing cartilage, and another one on either 

 side of the dorsal radial. Similar cartilages are to be found 

 ventrally in a corresponding position. This caudal fin, therefore, 

 will be regarded as ;i highly specinlized homocercal tvpe. 



