One distinctive bone may represent the basal plate of the posterior dorsal fin. This incomplete specimen shows two projecting curved processes, bearing low but distinct ridges, which diverge, probably anteriorly. The central portion is narrow. The two ridges continue onto the posterior portion. This has been broken off, but shows that the ridges diverge again. The surface is smooth, except for the ridges. As before, orientation is uncertain. On no. 786F this fin was interpreted by Hibbard (1933:281) as the anal fin.
Only part of one basal plate of the anal fin was preserved on K. U. no. 11450. That plate is oblong and has an expanded anterior end. The narrow, constricted part bears two oblique ridges and a few tubercles. The posterior part has nearly straight margins (represented by impressions) and the posterior margin is oblique, sloping anteroventrally. The flared anterior part has a smooth surface. This basal plate is more nearly like those of Coelacanthus, according to the descriptions given by Moy-Thomas (1937:399). The basal plate is associated with seven apparently unjointed, incomplete lepidotrichia. The anal fin on no. 786F is interpreted as the anterior dorsal fin (Hibbard, 1933:281).
The caudal fins are preserved on K. U. nos. 786F, 787F, and have a total of 24 lepidotrichia, 12 above and 12 below. These are jointed for the distal half or two-thirds, and are up to 16.0 mm. in length. In specimen no. 787F the supplementary caudal fin has at least seven lepidotrichia, the longest of which is 11.0 mm. but incomplete. Anterior lepidotrichia appear unjointed but the posterior ones are jointed for the distal two-thirds (?) (these are broken off). The supplementary caudal fin is approximately 1.5 mm. long and 8.0 mm. or more wide. The supplementary caudal fin on K. U. no. 786F described by Hibbard (1933:281) could not be observed; this part of the caudal fin is missing.
Squamation
In the suite of specimens isolated scales are numerous, but patches of scales are rare. Only two specimens (K. U. nos. 786F, 787F) are complete enough for scale counts, but preservation permits only partial counts. In general the scales resemble those of Rhabdoderma elegans (Newberry).
The scales are oval. The exposed posterior part of each bears posteriorly converging ridges; the anterior part is widest and shows a fine fibrillar structure. There are at least six scale-rows on either side of the lateral line. Lateral line scales show no pores, and except for slight irregularities in the orientation and length of the posterior ridges, closely resemble the others. Central ridges on the lateral line scales are shorter and tend to diverge from the center of the impression of the canal. The lateral line canal shows only as the impression of a continuous canal 0.7 mm. in diameter. Preservation is poorest in scales along the line of the neural and haemal arches; therefore lateral line scales are rarely preserved. Isolated scales are of two types: those on which the posterior ridges converge sharply and form the gothic arch configuration mentioned by Hibbard (1933:282), and those which do not. Both types of scales can be present on one fish, as shown by specimen no. 788. This is not apparent on nos. 786F and 787F; all of the scales on these specimens appear to be much alike. Both Moy-Thomas (1937:385) and Schaeffer (1952:51, 52) have remarked on the variation of the scales on different parts of the same fish. Because the number of ridges and amount of convergence of the ridges is not related to size of the scale, it is concluded that these characters are not of taxonomic significance.
The strong resemblance of the scales of the Garnett specimens to those of Rhabdoderma elegans (Newberry) caused Moy-Thomas (1937:399) to add Hibbard's two species to the synonymy of R. elegans. But at that time only the scales could be adequately described. If the shape of the scale and the number and pattern of ridges can vary with age, size and shape of the scale, it follows that assignment of isolated scales to a species should not be attempted. Assignment to genus should be made only with caution.
Discussion.—The relationship of Synaptotylus to other coelacanths is obscure at present. The knoblike antotic processes on the basisphenoid are unlike those of any other known coelacanth. The palatoquadrate complex is shaped like that of Rhabdoderma elegans but consists of fewer bones, probably because of fusion. The scales resemble those of Rhabdoderma. With regard to general shape of fin girdles, the pectoral girdle resembles that of Eusthenopteron more than that of Rhabdoderma, but the cleithrum is more nearly like the cleithrum of Rhabdoderma. The pelvic girdle appears to be midway between those of Rhabdoderma and Coelacanthus in general appearance. Regarding the basal plates of the remaining fins, those of Synaptotylus appear to resemble basal plates of both Rhabdoderma and Coelacanthus. Considering the structure of the sphenethmoid region of the braincase, Synaptotylus is probably more closely related to Rhabdoderma than to other known coelacanth genera.