138 WEALDEN AND PITRBECK FOSSIL FISHES. 



strengthened by a ridge extending diagonally from its antero-superior angle. The 

 supraclavicle is relatively deep and narrow, and the clavicle is much arched. 

 The anal fin comprises 27 rays, with three gradually lengthening fulcral rays in 

 front, and its anterior acumination is about three-quarters as deep as the trunk at 

 its insertion. The dorsal fin is slightly less elevated, with only 10 ordinary rays 

 preceded by three fulcrals. Traces of the usual thin scales are seen, none with 

 ornament. 



Remarks. — Although the abdominal part of the vertebral column in the type 

 specimen is somewhat displaced by crushing, the •arrangement of the neural arches 

 and ribs suggests that it has not been much shortened. The species is therefore 

 peculiar in the shortness of the trunk, and it differs from the only known species 

 from Portland (T. portlandicvs, A. S. Woodward, Catal. Foss. Fishes, Brit. Mus., 

 pt. iii, 1895, p. 525, pi. xviii, fig. 4) not only in this feature, but also in the more 

 remote insertion of the dorsal fin. 



Horizon and Locality. — Lower Purbeck Beds: Isle of Portland. The strati- 

 graphical position was determined by the collector of the type specimen, Mr. .J. R. 

 Short. The exact horizon of 7 '. portlandicus was not recorded by the collector. 



2. Thrissops molossus, sp. nov. Plate XXVI, fig. 2. 



Type. — Imperfect fish ; British Museum. 



Specific Characters. — At least 35 cm. in length. Head remarkably short and 

 deep. Length of head with opercular apparatus nearly equalling maximum depth 

 of trunk, and about one-fifth of total length of fish ; maximum depth of trunk 

 contained about three-and-a-half times in length from pectoral arch to base of 

 caudal fin. Caudal fin very deeply forked and lobes slender. 



Description <>l' Specimen. — There is no doubt that the fragmentary fish shown 

 of one-half the natural size in PI. XXVI, fig. 2, represents a hitherto unrecognised 

 species, but it is too imperfect for precise determination. The cranium is lacking, 

 but the adjacent remains are sufficiently undisturbed to show that the head is 

 unusually short and deep. The ossified border of the sclerotic of the very large 

 eye is well preserved, and the mandibular suspensorium and jaws are also seen. 

 The stout rod-shaped symplectic occurs below the hyomandibular, evidently fitting 

 into a cleft of the large fan-shaped quadrate. The pterygoid bones form an 

 extensive laminar expansion above the maxilla, which is gently arched and bears 

 a regular close series of small conical teeth. Of the premaxilla only a fragment 

 remains. The mandible is very imperfect, but its articulation is clearly below the 

 hinder border of the orbit, and its oral border bears conical teeth which are larger 

 than those of the maxilla. The remains of the operculum are bordered behind by 

 part of the clavicle, and its width is thus shown to equal half the length of the 



