PACHYTHRISSOPS. 129 



extended ; caudal fin deeply forked. Scales very delicate, often not preserved 

 in the fossils. 



Type Species. — Pachythrissops lasvis, from the English Pnrbeck Beds. 



Remarks. — The two species defined below were originally referred in error to 

 Oligoplenrus, and are proved by the new specimens now described to belong to 

 the Leptolepidse. They seem to be generically identical with a fish from the 

 Lithographic Stone of Bavaria named Parathrissops furcatus by Eastman (Mem. 

 Carnegie Mus. Pittsburgh, vol. vi, 1914, p. 423, pi. lix, fig. 2), which is distinguished 

 by the characters of its dorsal and anal fins. The generic name Parathrissops, 

 however, is preoccupied by Sauvage (Bull. Soc. Sci. Yonne, vol. xlv, pt. ii, 1891, 

 p. 37). The species also bear some resemblance to Eurystethus brongniarti (H. E. 

 Sauvage, Bull. Soc. Geol. France [3], vol. vi, 1878, p. 629, pi. xiii, fig. 2), from the 

 Kimmeridgian of Morestel, Ain, France, but this fish is too imperfectly known for 

 precise comparison. 



1 . Pachythrissops lsevis, sp. nov. Plate XXIV, figs. 3 — 5 ; Plate XXV, figs. 1 — 3. 



1890. Oligopleiirus (?) vectensis, A. S. Woodward, Proc. Zool. Soc, p. 346, pi. xxviii, tigs. 2 — 4, 

 pi. xxix, figs. 1 — 3. 



Type.— -Immature fish ; British Museum. 



Specific Characters. — -The type species, probably attaining a length of 50 cm., 

 but usually smaller. Length of head with opercular apparatus much exceeding 

 maximum depth, also much exceeding distance between paired fins, and occupying 

 nearly one-quarter of total length of fish. Operculum smooth, but with slime-pit 

 defined by two ridges on outer face at point of suspension ; preoperculum with 

 few radiating ridges near the angle. Vertebras 35 in abdominal, nearly 30 in 

 caudal region ; the centra of the latter longer than the former, and marked by a 

 sharp lateral ridge. Dorsal and anal fins arising directly opposite, the former 

 with about 18, the latter with slightly more than 20 rays. 



Description of Specimens.— The type specimen (PI. XXV, fig. 1) is a small fish, 

 which must probably be regarded as immature. It is shown in direct side view, 

 apparently not distorted, but its vertebral axis is not well preserved, and the ribs 

 are scarcely seen. All the known larger specimens are fragmentary, and one of 

 these (PI. XXIV, fig. 4) was wrongly referred to Lepidotus minor by L. Agassiz, 

 Poiss. Foss., vol. ii, pt. i (1844), p. 269, pi. xxix c, fig. 12. 



The head is much crushed and broken in the type specimen, but enough is 

 clear both in this and other specimens to identify with the same species the roof 

 of a skull shown in PI. XXIV, fig. 3. Here the specimen is somewhat flattened 

 by vertical crushing, but the bones are complete as far forwards as the front of 

 the orbit. The occiput is well ossified, and its upper portion is formed by a supra- 

 occipital in the middle with a pair of epiotics at the sides. The supraoccipital 



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