. Bulletin. Natural history; Natuurlijke historie. EARLY JURASSIC SEMIONOTID FISHES 61. Fig. 20. 5. ampHcephalus. A, outline of body form; B, camera lucida drawing of dorsal ridge scales. Scale = 5 mm. Both figures based on the holotype YPM 8849. 20B), and the scale bases are the same size or smaller than the flank scales. The holotype of this species is preserved in rock taken from the edge of a slump, and it may be somewhat distorted. However, what is unusual about its shape is that the head is very large in proportion to its body, and the probable direction of distortion would only make the
. Bulletin. Natural history; Natuurlijke historie. EARLY JURASSIC SEMIONOTID FISHES 61. Fig. 20. 5. ampHcephalus. A, outline of body form; B, camera lucida drawing of dorsal ridge scales. Scale = 5 mm. Both figures based on the holotype YPM 8849. 20B), and the scale bases are the same size or smaller than the flank scales. The holotype of this species is preserved in rock taken from the edge of a slump, and it may be somewhat distorted. However, what is unusual about its shape is that the head is very large in proportion to its body, and the probable direction of distortion would only make the fish appear more slender than it really is, not change the proportion of head to body length. The holotype is very large, about 29 cm standard length, and the head takes up an unusually large proportion of its length, about one-third. The body itself and the caudal peduncle are both stocky (Fig. 20A). Neither the scales nor the fin rays are well enough preserved to count with confidence, but there appear to be about 13 vertical scale rows anterior to the pelvic fin and about 30 lateral line scales. These counts, though only from one individual, are out of the range of variation for most Semionotus and related genera. The fact that this individual is unusually proportioned, has low scale counts, and has unusual dorsal ridge scales justifies specific distinction even of this single individual. The skull is quite well preserved, with a good view of the skull roof, a single suborbital, open cheek region, the circumorbital series, and the jaw joint, all as described for other Newark semionotids (Olsen and McCune ms). Although I have designated no paratypes, I tentatively refer another specimen, collected by Redfield (YPM 6484), to this species. It is a large individual with a large head like the holotype, but its shape is too distorted for reliable measurement. I refer this specimen to S. amplicephalus on the basis of a single dorsal ridge scale, which is like that described above
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