on all but the last of the caudal vertebrae; neural spines 

 decreasing in length from the first to the eighth, but in- 

 creasing in length from the 9th to 10th. As the neural 

 spines of the first to sixth caudal vertebrae decrease in 

 height, they become laterally compressed into antero- 

 posteriorly extended plates. The neural spines of the first 

 to third caudal vertebrae are placed between, and ar- 

 ticulate by fibrous tissue with, the dorsal fin basal ptery- 

 giophores. The anterior edge of the neural spine of the 

 fourth caudal vertebra articulates by fibrous tissue with 

 the posterior edge of the 11th, or last, basal pterygio- 

 phores. The neural spine of the 9th caudal vertebra 

 elongates almost directly posteriorly to form a roof over 

 the 10th caudal vertebra for almost the entire length of 

 the centrum of the latter. The neural spine of the 10th 

 caudal vertebra is an elongate shaft which distally sup- 

 ports the first 4 or 5 procurrent caudal fin rays. The an- 

 terior ends of the neural arches and bases of the neural 

 spines of all of the caudal vertebrae, except for the last 

 two or three, are prolonged anterolaterally into thick 

 spinelike processes to which are attached large muscle 

 masses. Just above the centrum on the lower anterior 

 edge of the neural arch there is a shorter anterior process 

 which articulates by fibrous tissue with the postero- 

 lateral surface of the neural arch and base of the neural 

 spine of the preceding vertebra. This anterior process, 

 representing the neural prezygapophysis, is increasingly 

 well developed from the first to about the fifth and sixth 

 caudal vertebrae, posterior to which it becomes 

 progressively smaller again. The haemal arches and 

 spines of the first to fifth or sixth caudal vertebrae bear 

 epipleurals laterally and the first to fifth support through 

 fibrous tissue ventrally the basal pterygiophores of the 

 anal fin. Along most of its posterior edge the haemal 

 spine of the first caudal vertebra supports the upper an- 

 terior edge of the enlarged first basal pterygiophore of the 

 anal fin. The haemal spines of the second to fourth 

 caudal vertebrae support most of the anal fin basal 

 pterygiophores. The posterolaterally expanded and 

 slightly concave anterior surface of the large haemal 

 spine of the fifth caudal vertebra supports the small 

 ninth, or last, pterygiophore. The ventrolateral surface of 

 the posterior half of each centrum from the first to fifth 

 caudal vertebrae becomes increasingly expanded ven- 

 trally to form the side walls of the trough through which 

 the haemal canal courses. At the sixth caudal vertebra 

 these ventral expansions articulate by fibrous tissue with 

 the dorsal edge of the posteriorly prolonged flange of the 

 haemal spine. There are thus, in effect, two arches over 

 the haemal canal — the haemal arch proper and the arch 

 formed by the meeting of the haemal spine with the ven- 

 tral flange from either side of the posteroventral surface 

 of the centrum. The seventh and eighth caudal verte- 

 brae have the same arrangement, except that the sur- 

 face of contact between the haemal spine and the ven- 

 tral flanges is fused, leaving only a foramen to indicate 

 what was formerly the wide space between the dorsal 

 edge of the posteriorly directed haemal spine and the 

 ventrolateral surface of the centrum. The haemal spine 

 of the 9th caudal vertebra, like its neural spine, is 



prolonged posteriorly to form a roof over the haemal arch 

 and base of the haemal spine of the 10th caudal verte- 

 bra. The haemal spine of the 10th caudal vertebra, like 

 its neural spine, forms a long shaft that distally supports 

 most of the procurrent rays of the lower lobe of the caudal 

 fin. The haemal arches and spines of the 9th and 10th 

 caudal vertebrae are autogenous. 



Caudal Skeleton. — The caudal fin supporting struc- 

 tures are composed of the Uth caudal vertebra and its 

 urostylar projection, an epural, two pairs of uroneurals, 

 four hypurals, and a parhypural, as well as the shaftlike 

 neural spine and haemal spine of the 10th caudal verte- 

 bra. The centrum of the 11th caudal vertebra is prolong- 

 ed posterodorsally into a urostylar process whose pos- 

 terior edge is concave and supports the upper three 

 hypurals, while its anterodorsal edge is similarly con- 

 cave and helps support the uroneurals. Because of its 

 concave anterodorsal and posterior surfaces, the upper 

 half of the urostyle is forked into right and left halves, 

 since there is no bony material in the midline of the uro- 

 style in this region. From the anterolateral region of its 

 dorsal surface the centrum possesses an anteriorly 

 directed prong or neural prezygapophysis which ar- 

 ticulates by fibrous tissue with the posterolateral sur- 

 face of the neural spine of the 10th caudal vertebra. The 

 dorsomedial edges of the two sides of the neural arch of 

 the last centrum are not in close contact in the midline 

 over the neural canal, only partially roofing over the lat- 

 ter. The epural is a large column of bone which is con- 

 cave along the upper half of its posterior edge. It ar- 

 ticulates by fibrous tissue anteriorly with the posterior 

 edge of the neural spine of the 10th caudal vertebra, pos- 

 teriorly with the first uroneural and ventrally with the 

 dorsal edges of the incomplete neural arch of the 11th 

 caudal vertebra. The second uroneural is a long rounded 

 shaft, with a medial groove along its length representing 

 the region of complete fusion of its two halves, whose 

 anteroventral edge rests against the concave dorsal sur- 

 face of the urostyle mainly in the region of its pwsterior 

 bifurcation. The posterodorsal end of the second 

 uroneural supports the deeply forked base of the first 

 principal ray of the upper lobe of the caudal fin. Along 

 the ventral two-thirds of its round anterior surface the 

 second uroneural has closely applied to it a large, but 

 very thin, pair of bones, the first uroneurals, which ar- 

 ticulate with it, and with each other medially, by fibrous 

 tissue. Along their anteroventral edges the first uro- 

 neurals articulate by fibrous tissue with the dorsal sur- 

 face of the neural arch and urostyle of the last centrum. 

 The fourth hypural, or uppermost, is more or less 

 triangular in shape, with the lower two-thirds of its an- 

 terior edge resting against the concave posterior surface 

 of the urostyle. Along its ventral edge the fourth hypural 

 is closely held by fibrous tissue to the dorsal edge of the 

 third hypural. The third hypural is widest posteriorly, 

 narrow anteriorly to a slightly convex and laterally ex- 

 panded articular facet which fits against a concavity on 

 the anterior one-third of the dorsal edge of the second 

 hypural. The extreme anterior end of the second hypural 



