caudal vertebrae except the last, possess bony roofs over 

 the neural canal and have single, undivided neural 

 spines. The neural spines of the abdominal vertebrae are 

 all of about the same length but they are of increasing 

 width posteriorly in the series. Their edges of apposition 

 articulate with one another through fibrous tissue and, in 

 some cases, slight interdigitation. Each neural arch has a 

 neural foramen in its lateral surface. Haemal prezyga- 

 pophyses are weakly developed on a few vertebrae, but 

 mostly they are absent or insignificant. Except for the 

 first, all of the abdominal vertebrae have transverse 

 processes which bear epipleural ribs. These processes 

 become increasingly laterally expanded and stouter pos- 

 teriorly in the series. The transverse process of the second 

 vertebra arises in about the middle of the anterior region 

 of the centrum, but the transverse processes of the subse- 

 quent vertebrae originate low on the centrum. The 

 epipleurals articulate by fibrous tissue to the dorso- 

 lateral surfaces of the transverse processes. The trans- 

 verse processes of the fifth and sixth abdominal 

 vertebrae have posteromedial flanges from each side 

 which make contact with the haemal regions of the 

 succeeding vertebrae, roofing over the haemal canal un- 

 der the fifth and sixth vertebrae, while more anteriorly 

 the haemal canal is open. The first basal pterygiophore of 

 the soft dorsal fin articulates between the neural spines 

 of the fourth and fifth vertebrae, the articulation being 

 by fibrous tissue. The second basal pterygiophore of the 

 soft dorsal fin articulates similarly between the neural 

 spines of the fifth and sixth abdominal vertebrae. 



Caudal Vertebrae. —The caudal vertebrae number 11 

 in 12 specimens. The neural spines of the caudal 

 vertebrae become less expanded anterodorsally and in- 

 creasingly shorter posteriorly in the series, except for the 

 last few vertebrae, behind the soft dorsal and anal fin 

 bases, which have the neural and haemal spines expand- 

 ed. All of the caudal vertebrae, except for the last, 

 possess complete neural and haemal arches and spines. 

 Haemal pre- and postzygapophyses are essentially ab- 

 sent, but neural pre- and postzygapophyses are distinctly 

 developed in both the caudal and abdominal series. The 

 sturdy haemal spine of the first caudal vertebra is 

 somewhat concave ventrally along its posterior surface 

 and slightly bifurcate at its extreme distal end. It is 

 against the posterior surface of this haemal spine that 

 the first basal pterygiophore of the anal fin is firmly held 

 by fibrous tissue. The haemal spines of the second and 

 third caudal vertebrae are progressively slightly longer 

 than that of the first, but more posteriorly the length of 

 the spines decreases until those of the 10th to 12th 

 vertebrae, which are of increased length. The length of 

 the neural spine similarly decreases posteriorly in the 

 series and then increases behind the soft dorsal fin base. 

 The haemal spine of the penultimate vertebra is auto- 

 genous. The haemal and neural spines of the last caudal 

 vertebra are described below. 



Caudal Skeleton. — The caudal complex usually 



consists of an epural, a free parhypural, and a large plate 

 composed of the centrum fused to the hypural elements. 

 The free epural and parhypural are of about equal size. 

 The neural arch of the last centrum is incomplete, the 

 neural canal not being roofed over. Similarly the haemal 

 canal is not roofed over and its presence is simply in- 

 dicated by an indentation in the anteroventral edge of 

 the hypural plate just below the centrum and above the 

 dorsal end of the parhypural. The fused hypural plate 

 bears a horizontal keel for muscle attachment on the rear 

 portion of the centrum area and anterior region of the 

 fused hypurals. There is also a deep indentation on the 

 middle of the posterior edge of the fused plate, this in- 

 dentation representing what would be the division 

 between the second and third hypurals in a more 

 generalized plectognath having five free hypurals. The 

 above is the condition found in 10 of the 12 study 

 specimens. However, as described and illustrated by 

 Tyler (1970b:16, fig. 31), 2 of the 12 specimens have an 

 upper free hypural, representing the fifth hypural of 

 generalized plectognaths. The presence of an upper free 

 hypural is the norm for the family, all species examined 

 having one with the exception of, usually, M. ciliatus, 

 and the several specimens of Rudarius ercodes and 

 R. minutus cleared and stained or radiographed, and 

 the single specimen of Amanses scopas cleared and 

 stained. 



Caudal fin ra.vs. — Twelve in number; the uppermost 



ray and the lowermost ray unbranched, the others 

 becoming increasingly branched toward the middle fin 

 rays, which are branched in triple dichotomies. The bifid 

 bases of the fin rays articulate by fibrous tissue with the 

 caudal skeleton as follows: the upper six rays to the up- 

 per half of the fused hypural plate and the lower six rays 

 to the lower half of the plate. 



DORSAL AND ANAL FINS. 



Dorsal Fin 



Spines and pterygiophores. — Two spines borne on a 

 large and elongate basal pterygiophore. First spine long 

 and moderately stout; second spine much smaller, con- 

 sisting of a basal rounded region, a slender tapering dis- 

 tal end and, from the ventrolateral edge of the basal ex- 

 panded region, a laterally projecting flange for muscle 

 attachment. The concave ventromedial region of the first 

 spine rotates over a low medial flange on the pterygio- 

 phore, while posteromedially the first spine has a ven- 

 trally directed flange which rotates into a deep concavity 

 on the basal pterygiophore just behind the medial flange. 

 The thick posterior region of this posteromedial flange of 

 the first spine is roughened and makes contact with the 

 similarly roughened anterior edge of the basally expand- 

 ed portion of the second spine to form the locking 

 mechanism. The concave ventral surface of the second 

 spine rotates over a low medial flange on the pterygio- 



143 



