roof over the neural canal on the first to ninth ab 

 dominal vertebrae. The 10th and Uth abdominal verte 

 brae have no such bony roof over the neural canal, the 

 canal being roofed over between the divergent neura 

 spines of these two vertebrae only by fibrous tissue. The 

 dorsomedial region of the bony roof over the neural cana 

 becomes upraised into what is, in effect, a third neura 

 spine on some of the abdominal vertebrae. There is only 

 a trace of such a dorsomedial flange on the third ab 

 dominal vertebra but on the fourth abdominal vertebra it 

 is distinctly present, and by the fifth and sixth ab 

 dominal vertebrae it reaches its maximum develop 

 ment, then becomes progressively less well developed on 

 the seventh and eighth abdominal vertebrae until by the 

 ninth abdominal vertebra it is no longer present. At its 

 greatest development, on the fifth and sixth abdominal 

 vertebrae, this dorsomedial flange is prolonged an- 

 teriorly to such an extent that it protrudes over the pos- 

 terior region of the neural arch of the preceding verte- 

 bra, with fibrous tissue attaching it to the bony roof over 

 the neural canal. Neural prezygapophyses are well 

 developed on all of the abdominal vertebrae and ar- 

 ticulate by fibrous tissue with the posterodorsal regions 

 of the lateral surfaces of the centrum just anterior to 

 them. Haemal arches are not present on any of the ab- 

 dominal vertebrae, but from the 9th to 12th abdominal 

 vertebrae progressively larger ventrolateral flanges are 

 present from the ventrolateral edges of the centra. These 

 flanges are the place of attachment of large muscle 

 masses. The 12th abdominal vertebra differs from the 

 other abdominal vertebrae in that its neural arch does 

 not possess a bifid and divergent neural spine. From the 

 base of its neural arch area two broad plates project dor- 

 sally and slightly medially to meet the bases of the first 

 two dorsal fin basal pterygiophores. There is no distinct 

 bony roof over the neural canal of the 12th abdominal 

 vertebra, the functional roof being formed by the fibrous 

 tissue articulation of the ventral ends of the basal pteryg- 

 iophores with the dorsal ends of the lateral walls of the 

 neural arches. 



Caudal Vertebrae. — Nine caudal vertebrae in 10 

 specimens; the first six caudal vertebrae variously sup- 

 porting the dorsal and anal fin basal pterygiophores. The 

 first three caudal vertebrae are structurally similar to the 

 last abdominal vertebra, but their ventrolateral flanges 

 become progressively shorter, and delicate posteroven- 

 trally directed processes from the ventrolateral surfaces 

 of their centra are present which articulate by fibrous tis- 

 sue with the dorsal ends of the anal fin basal pterygio- 

 phores. As is the case with the last abdominal vertebra, 

 the lateral walls of the neural arches of the first three 

 caudal vertebrae articulate by fibrous tissue dorsally 

 with the ventral ends of the dorsal fin basal pterygio- 

 phores. The fourth caudal vertebra differs from the 

 preceding caudal vertebrae by the only slight develop- 

 ment of its ventrolateral flange, and by the presence 

 along the posterior half of the dorsal surface of its neural 

 arch of a bifid and divergent neural spine. The anterior 

 half of the dorsal surface of this neural arch possesses the 



dorsomedially directed bony plates which articulate by 

 fibrous tissue with the bases of the last two dorsal fin 

 basal pterygiophores, in the same way as described for 

 the preceding caudal vertebrae. From its posteroventral 

 edge the fourth caudal vertebra possesses a short pos- 

 terior process which articulates by fibrous tissue with an 

 anteriorly directed prong from the haemal process of the 

 fifth caudal vertebra. The fifth caudal vertebra possesses 

 a bifid and divergent neural spine between which is sup- 

 ported by fibrous tissue the last dorsal fin basal ptery- 

 giophore, with no bony roof present over the neural canal 

 between the medial edges of its divergent neural spine. 

 Delicate ventral processes are present from the ventro- 

 lateral edges of the fifth caudal vertebra which support 

 the dorsal end of the last anal fin basal pterygiophore, 

 while a bifid and divergent haemal process is present 

 ventrally to either side of the upper end of the last anal 

 fin basal pterygiophore. There is no special bony roof 

 over the haemal canal, except the functional one formed 

 by the ventral processes of the fifth caudal vertebra 

 meeting with the dorsal end of the last anal fin basal 

 pterygiophore. The anterior edge of the bifid haemal 

 process is produced into a short prong which articulates 

 by fibrous tissue with the posterior process from the 

 fourth caudal vertebra. The sixth and seventh caudal 

 vertebrae are similar to one another, their centra being 

 relatively short anteroposteriorly and both possessing 

 bifid neural and haemal spines. No bony roofs are present 

 between these bifid neural and haemal spines, so that the 

 neural and haemal canals are roofed over only by fibrous 

 tissue. The anterior edges of the neural and haemal 

 spines of the sixth caudal vertebra support by fibrous tis- 

 sue, respectively, the last dorsal fin basal pterygiophore 

 and the last anal fin basal pterygiophore. The eighth 

 caudal vertebra has its neural and haemal spines bifid 

 and divergent anteriorly, but as single medial plates pos- 

 teriorly. The undivided posterior portions of the neural 

 and haemal spines of this vertebra are posteriorly ex- 

 panded, and they interdigitate with the anterior edge of 

 the plate formed by the last vertebra and associated 

 caudal fin supporting elements. From the lateral surface 

 of the haemal spine of the eighth abdominal vertebra, a 

 posteriorly directed process is present which articulates 

 by fibrous tissue with the anteriorly directed process 

 from the last vertebral segment. 



Caudal Skeleton. — The caudal fin supporting struc- 

 tures are consolidated into a single plate which in adults 

 shows only meager traces of areas of suturing or fusion of 

 the originally separate elements. In specimens smaller 

 than about 100 mm, however, at least one of the elements 

 retains its individuality, this being the epural. The 

 elongate epural is interdigitated with the posterior edge 

 of the neural spine of the eighth caudal vertebra and with 

 the anterodorsal edge of the main portion of the plate 

 supporting the caudal fin. In larger specimens the sutur- 

 ing between these two elements becomes obscure and 

 true fusion may take place. Anteroventrally on the 

 caudal plate in the smaller study specimens there is some 

 indication of an originally separate parhypural having 



